Change description of destination_project field in backup and restore channel resources. (GoogleCloudPlatform#13945)

Author: aru31

mmv1/products/gkebackup/BackupChannel.yaml

@@ -78,7 +78,7 @@ properties:
     description: |
       The project where Backups are allowed to be stored.
       The format is `projects/{project}`.
-      {project} can only be a project number.
+      {project} can be project number or project id.
     required: true
     immutable: true
   - name: 'description'

mmv1/products/gkebackup/RestoreChannel.yaml

@@ -78,7 +78,7 @@ properties:
     description: |
       The project where Backups will be restored.
       The format is `projects/{project}`.
-      {project} can only be a project number.
+      {project} can be project number or project id.
     required: true
     immutable: true
   - name: 'description'