[CLD-7046] Ability to disable self hosted server-side requests to CWS (#26070)

* Add 'Disable' config to CloudSettings to prevent the CWS backend from making calls to the Customer Portal

* Add custom error when disabled

* Make Disable setting cloud_restrictable

* Return 422 instead of 400

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Co-authored-by: Mattermost Build <build@mattermost.com>

server/i18n/en.json

@@ -2762,6 +2762,10 @@
     "id": "api.server.cws.delete_workspace.app_error",
     "translation": "CWS Server failed to delete workspace."
   },
+  {
+    "id": "api.server.cws.disabled",
+    "translation": "Interactions with the Mattermost Customer Portal have been disabled by the system admin."
+  },
   {
     "id": "api.server.cws.health_check.app_error",
     "translation": "CWS Server is not available."