Allow managing members in the project resource (#480)

* Extend resource and datasource

* Adapt acc test to work without members

* Extend acc test and adjust resource

* Generate docs

* Fix lint

* Fix unit test

* Uniformize description with datasource and extend unit test

* Improve role field description

* Update TF state before adding/removing members

* Remove unused function

* Move intermediate map top state to mapProjectFields

* Improve code

stackit/internal/validate/validate.go

@@ -14,6 +14,7 @@ import (
 	"github.com/hashicorp/terraform-plugin-framework/schema/validator"
 	"github.com/hashicorp/terraform-plugin-framework/types/basetypes"
 	"github.com/stackitcloud/terraform-provider-stackit/stackit/internal/core"
+	"github.com/stackitcloud/terraform-provider-stackit/stackit/internal/utils"
 	"github.com/teambition/rrule-go"
 )
 
@@ -137,6 +138,23 @@ func NoSeparator() *Validator {
 	}
 }
 
+func NonLegacyProjectRole() *Validator {
+	description := "legacy roles are not supported"
+
+	return &Validator{
+		description: description,
+		validate: func(ctx context.Context, req validator.StringRequest, resp *validator.StringResponse) {
+			if utils.IsLegacyProjectRole(req.ConfigValue.ValueString()) {
+				resp.Diagnostics.Append(validatordiag.InvalidAttributeValueDiagnostic(
+					req.Path,
+					description,
+					req.ConfigValue.ValueString(),
+				))
+			}
+		},
+	}
+}
+
 func MinorVersionNumber() *Validator {
 	description := "value must be a minor version number, without a leading 'v': '[MAJOR].[MINOR]'"