Is your feature request related to a problem? Please describe.

There is currently no way to temporarily pause federation links without deleting the upstream definition or the policy that triggers them. When performing maintenance on an upstream broker, debugging message flow, or needing to temporarily halt federation for operational reasons, the only option is to remove the policy or upstream parameter entirely and recreate it afterwards. This is error-prone and disruptive. Recreating policies and upstreams risks misconfiguration, and any in-flight messages may be lost or duplicated during the teardown/rebuild cycle.

Describe the solution you'd like
Add the ability to pause and resume individual federation links (or all links for a given upstream) through the HTTP API. A paused link would cleanly disconnect from the upstream broker and stop consuming messages, but retain its full configuration so it can be resumed without any reconfiguration.

  PUT /api/federation-links/:vhost/:id/pause
  PUT /api/federation-links/:vhost/:id/resume

Or at the upstream level:

PUT /api/parameters/federation-upstream/:vhost/:name { ..., "paused": true }

A paused link should show status: "paused" in the GET /api/federation-links response so operators have clear visibility into link state.