add link to the available service plans page (#575)

docs/data-sources/volume.md

@@ -37,7 +37,7 @@ data "stackit_volume" "example" {
 - `id` (String) Terraform's internal resource ID. It is structured as "`project_id`,`volume_id`".
 - `labels` (Map of String) Labels are key-value string pairs which can be attached to a resource container
 - `name` (String) The name of the volume.
-- `performance_class` (String) The performance class of the volume.
+- `performance_class` (String) The performance class of the volume. Possible values are documented in [Service plans BlockStorage](https://docs.stackit.cloud/stackit/en/service-plans-blockstorage-75137974.html#ServiceplansBlockStorage-CurrentlyavailableServicePlans%28performanceclasses%29)
 - `server_id` (String) The server ID of the server to which the volume is attached to.
 - `size` (Number) The size of the volume in GB. It can only be updated to a larger value than the current size
 - `source` (Attributes) The source of the volume. It can be either a volume, an image, a snapshot or a backup (see [below for nested schema](#nestedatt--source))

docs/resources/volume.md

@@ -40,7 +40,7 @@ resource "stackit_volume" "example" {
 - `description` (String) The description of the volume.
 - `labels` (Map of String) Labels are key-value string pairs which can be attached to a resource container
 - `name` (String) The name of the volume.
-- `performance_class` (String) The performance class of the volume.
+- `performance_class` (String) The performance class of the volume. Possible values are documented in [Service plans BlockStorage](https://docs.stackit.cloud/stackit/en/service-plans-blockstorage-75137974.html#ServiceplansBlockStorage-CurrentlyavailableServicePlans%28performanceclasses%29)
 - `server_id` (String) The server ID of the server to which the volume is attached to.
 - `size` (Number) The size of the volume in GB. It can only be updated to a larger value than the current size. Either `size` or `source` must be provided
 - `source` (Attributes) The source of the volume. It can be either a volume, an image, a snapshot or a backup. Either `size` or `source` must be provided (see [below for nested schema](#nestedatt--source))

stackit/internal/services/iaas/volume/datasource.go

@@ -139,8 +139,8 @@ func (r *volumeDataSource) Schema(_ context.Context, _ datasource.SchemaRequest,
 				Computed:    true,
 			},
 			"performance_class": schema.StringAttribute{
-				Description: "The performance class of the volume.",
-				Computed:    true,
+				MarkdownDescription: "The performance class of the volume. Possible values are documented in [Service plans BlockStorage](https://docs.stackit.cloud/stackit/en/service-plans-blockstorage-75137974.html#ServiceplansBlockStorage-CurrentlyavailableServicePlans%28performanceclasses%29)",
+				Computed:            true,
 			},
 			"size": schema.Int64Attribute{
 				Description: "The size of the volume in GB. It can only be updated to a larger value than the current size",

stackit/internal/services/iaas/volume/resource.go

@@ -229,9 +229,9 @@ func (r *volumeResource) Schema(_ context.Context, _ resource.SchemaRequest, res
 				Optional:    true,
 			},
 			"performance_class": schema.StringAttribute{
-				Description: "The performance class of the volume.",
-				Optional:    true,
-				Computed:    true,
+				MarkdownDescription: "The performance class of the volume. Possible values are documented in [Service plans BlockStorage](https://docs.stackit.cloud/stackit/en/service-plans-blockstorage-75137974.html#ServiceplansBlockStorage-CurrentlyavailableServicePlans%28performanceclasses%29)",
+				Optional:            true,
+				Computed:            true,
 				PlanModifiers: []planmodifier.String{
 					stringplanmodifier.RequiresReplace(),
 					stringplanmodifier.UseStateForUnknown(),