chore: changed and refactored providers (#36)

## Description

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relates to #1234

## Checklist

- [ ] Issue was linked above
- [ ] Code format was applied: `make fmt`
- [ ] Examples were added / adjusted (see `examples/` directory)
- [x] Docs are up-to-date: `make generate-docs` (will be checked by CI)
- [ ] Unit tests got implemented or updated
- [ ] Acceptance tests got implemented or updated (see e.g. [here](f5f99d1709/stackit/internal/services/dns/dns_acc_test.go))
- [x] Unit tests are passing: `make test` (will be checked by CI)
- [x] No linter issues: `make lint` (will be checked by CI)

Co-authored-by: Marcel S. Henselin <marcel.henselin@stackit.cloud>
Reviewed-on: #36
Reviewed-by: Marcel_Henselin <marcel.henselin@stackit.cloud>
Co-authored-by: Andre Harms <andre.harms@stackit.cloud>
Co-committed-by: Andre Harms <andre.harms@stackit.cloud>

docs/data-sources/postgresflexalpha_flavors.md

@@ -38,12 +38,12 @@ Read-Only:
 
 - `cpu` (Number) The cpu count of the instance.
 - `description` (String) The flavor description.
-- `id` (String) The id of the instance flavor.
 - `max_gb` (Number) maximum storage which can be ordered for the flavor in Gigabyte.
 - `memory` (Number) The memory of the instance in Gibibyte.
 - `min_gb` (Number) minimum storage which is required to order in Gigabyte.
 - `node_type` (String) defines the nodeType it can be either single or replica
 - `storage_classes` (Attributes List) maximum storage which can be ordered for the flavor in Gigabyte. (see [below for nested schema](#nestedatt--flavors--storage_classes))
+- `tf_original_api_id` (String) The id of the instance flavor.
 
 <a id="nestedatt--flavors--storage_classes"></a>
 ### Nested Schema for `flavors.storage_classes`

docs/data-sources/postgresflexalpha_instance.md

@@ -37,7 +37,6 @@ data "stackitprivatepreview_postgresflexalpha_instance" "example" {
 
 ⚠︝ **Note:** This feature is in private preview. Supplying this object is only permitted for enabled accounts. If your account does not have access, the request will be rejected. (see [below for nested schema](#nestedatt--encryption))
 - `flavor_id` (String) The id of the instance flavor.
-- `id` (String) The ID of the instance.
 - `is_deletable` (Boolean) Whether the instance can be deleted or not.
 - `name` (String) The name of the instance.
 - `network` (Attributes) The access configuration of the instance (see [below for nested schema](#nestedatt--network))
@@ -45,6 +44,7 @@ data "stackitprivatepreview_postgresflexalpha_instance" "example" {
 - `retention_days` (Number) How long backups are retained. The value can only be between 32 and 365 days.
 - `status` (String) The current status of the instance.
 - `storage` (Attributes) The object containing information about the storage size and class. (see [below for nested schema](#nestedatt--storage))
+- `tf_original_api_id` (String) The ID of the instance.
 - `version` (String) The Postgres version used for the instance. See [Versions Endpoint](/documentation/postgres-flex-service/version/v3alpha1#tag/Version) for supported version parameters.
 
 <a id="nestedatt--connection_info"></a>

docs/data-sources/sqlserverflexalpha_database.md

@@ -26,6 +26,6 @@ description: |-
 
 - `collation_name` (String) The collation of the database. This database collation should match the *collation_name* of one of the collations given by the **Get database collation list** endpoint.
 - `compatibility_level` (Number) CompatibilityLevel of the Database.
-- `id` (Number) The id of the database.
 - `name` (String) The name of the database.
 - `owner` (String) The owner of the database.
+- `tf_original_api_id` (Number) The id of the database.

docs/data-sources/sqlserverflexalpha_instance.md

@@ -34,7 +34,6 @@ data "stackitprivatepreview_sqlserverflexalpha_instance" "example" {
 - `edition` (String) Edition of the MSSQL server instance
 - `encryption` (Attributes) this defines which key to use for storage encryption (see [below for nested schema](#nestedatt--encryption))
 - `flavor_id` (String) The id of the instance flavor.
-- `id` (String) The ID of the instance.
 - `is_deletable` (Boolean) Whether the instance can be deleted or not.
 - `name` (String) The name of the instance.
 - `network` (Attributes) The access configuration of the instance (see [below for nested schema](#nestedatt--network))
@@ -42,6 +41,7 @@ data "stackitprivatepreview_sqlserverflexalpha_instance" "example" {
 - `retention_days` (Number) The days for how long the backup files should be stored before cleaned up. 30 to 365
 - `status` (String)
 - `storage` (Attributes) The object containing information about the storage size and class. (see [below for nested schema](#nestedatt--storage))
+- `tf_original_api_id` (String) The ID of the instance.
 - `version` (String) The sqlserver version used for the instance.
 
 <a id="nestedatt--encryption"></a>

docs/data-sources/sqlserverflexbeta_instance.md

@@ -34,7 +34,6 @@ data "stackitprivatepreview_sqlserverflexbeta_instance" "example" {
 - `edition` (String) Edition of the MSSQL server instance
 - `encryption` (Attributes) this defines which key to use for storage encryption (see [below for nested schema](#nestedatt--encryption))
 - `flavor_id` (String) The id of the instance flavor.
-- `id` (String) The ID of the instance.
 - `is_deletable` (Boolean) Whether the instance can be deleted or not.
 - `name` (String) The name of the instance.
 - `network` (Attributes) The access configuration of the instance (see [below for nested schema](#nestedatt--network))
@@ -42,6 +41,7 @@ data "stackitprivatepreview_sqlserverflexbeta_instance" "example" {
 - `retention_days` (Number) The days for how long the backup files should be stored before cleaned up. 30 to 365
 - `status` (String)
 - `storage` (Attributes) The object containing information about the storage size and class. (see [below for nested schema](#nestedatt--storage))
+- `tf_original_api_id` (String) The ID of the instance.
 - `version` (String) The sqlserver version used for the instance.
 
 <a id="nestedatt--encryption"></a>