Adds params.resource_manager_tags to google_compute_region_commitment so IAM resource manager tags can be bound at commitment creation. The field is input-only and ForceNew, matching the existing pattern on google_compute_network (#14119) and other Compute resources.

The acceptance test has no `CheckDestroy` because `RegionCommitment` is `exclude_delete: true`; recording it creates a real, non-deletable multi-year commitment, so it should be recorded once on a sacrificial project and replayed in CI.

```release-note:enhancement
compute: added `params.resource_manager_tags` field to `google_compute_region_commitment` resource
```

Author: GitOleksandrBokov

mmv1/products/compute/RegionCommitment.yaml

@@ -203,3 +203,18 @@ properties:
     description: |
       Specifies the already existing reservations to attach to the Commitment.
     default_from_api: true
+  - name: 'params'
+    type: NestedObject
+    ignore_read: true
+    immutable: true
+    description: |
+     Additional params passed with the request, but not persisted as part of resource payload
+    properties:
+      - name: 'resourceManagerTags'
+        type: KeyValuePairs
+        description: |
+          Resource manager tags to be bound to the commitment. Tag keys and values have the
+          same definition as resource manager tags. Keys must be in the format tagKeys/{tag_key_id},
+          and values are in the format tagValues/456.
+        api_name: resourceManagerTags
+        ignore_read: true

mmv1/third_party/terraform/services/compute/resource_compute_region_commitment_test.go

@@ -0,0 +1,63 @@
+package compute_test
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/hashicorp/terraform-plugin-testing/helper/resource"
+	"github.com/hashicorp/terraform-provider-google/google/acctest"
+	"github.com/hashicorp/terraform-provider-google/google/envvar"
+)
+
+// WARNING: RECORDING this test creates a real, non-deletable multi-year commitment
+// (RegionCommitment has exclude_delete: true). Use VCR REPLAYING in CI; only RECORD
+// on a sacrificial project where orphaned commitments are acceptable.
+func TestAccComputeRegionCommitment_resourceManagerTags(t *testing.T) {
+
+	t.Parallel()
+
+	org := envvar.GetTestOrgFromEnv(t)
+	suffixName := acctest.RandString(t, 10)
+	tagKeyResult := acctest.BootstrapSharedTestTagKeyDetails(t, "crm-region-commitment-tagkey", "organizations/"+org, make(map[string]interface{}))
+	sharedTagkey, _ := tagKeyResult["shared_tag_key"]
+	tagValueResult := acctest.BootstrapSharedTestTagValueDetails(t, "crm-region-commitment-tagvalue", sharedTagkey, org)
+
+	context := map[string]interface{}{
+		"commitment_name": fmt.Sprintf("tf-test-commitment-rmt-%s", suffixName),
+		"tag_key_id":      tagKeyResult["name"],
+		"tag_value_id":    tagValueResult["name"],
+	}
+
+	acctest.VcrTest(t, resource.TestCase{
+		PreCheck:                 func() { acctest.AccTestPreCheck(t) },
+		ProtoV5ProviderFactories: acctest.ProtoV5ProviderFactories(t),
+		// No CheckDestroy: RegionCommitment has exclude_delete: true.
+		Steps: []resource.TestStep{
+			{
+				Config: testAccComputeRegionCommitment_resourceManagerTags(context),
+			},
+		},
+	})
+}
+
+func testAccComputeRegionCommitment_resourceManagerTags(context map[string]interface{}) string {
+	return acctest.Nprintf(`
+resource "google_compute_region_commitment" "foobar" {
+  name = "%{commitment_name}"
+  plan = "TWELVE_MONTH"
+  resources {
+    type   = "VCPU"
+    amount = "1"
+  }
+  resources {
+    type   = "MEMORY"
+    amount = "1"
+  }
+  params {
+    resource_manager_tags = {
+      "%{tag_key_id}" = "%{tag_value_id}"
+    }
+  }
+}
+`, context)
+}