feat: SQL server beta and templates refactoring (#32)

## Description

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At least please give us some description what you are trying to achieve and why your change is needed. -->

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)

Reviewed-on: #32
Reviewed-by: Andre_Harms <andre.harms@stackit.cloud>
Co-authored-by: Marcel S. Henselin <marcel.henselin@stackit.cloud>
Co-committed-by: Marcel S. Henselin <marcel.henselin@stackit.cloud>

docs/data-sources/sqlserverflexbeta_flavor.md

@@ -0,0 +1,47 @@
+---
+# generated by https://github.com/hashicorp/terraform-plugin-docs
+page_title: "stackitprivatepreview_sqlserverflexbeta_flavor Data Source - stackitprivatepreview"
+subcategory: ""
+description: |-
+  
+---
+
+# stackitprivatepreview_sqlserverflexbeta_flavor (Data Source)
+
+
+
+## Example Usage
+
+```terraform
+data "stackitprivatepreview_sqlserverflexbeta_flavor" "flavor" {
+  project_id    = var.project_id
+  region        = var.region
+  cpu           = 4
+  ram           = 16
+  node_type     = "Single"
+  storage_class = "premium-perf2-stackit"
+}
+```
+
+<!-- schema generated by tfplugindocs -->
+## Schema
+
+### 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 HA
+- `storage_classes` (Attributes List) maximum storage which can be ordered for the flavor in Gigabyte. (see [below for nested schema](#nestedatt--storage_classes))
+
+<a id="nestedatt--storage_classes"></a>
+### Nested Schema for `storage_classes`
+
+Read-Only:
+
+- `class` (String)
+- `max_io_per_sec` (Number)
+- `max_through_in_mb` (Number)