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`