FE: Handle 504s properly

[papirosko]

Issue submitter TODO list

• I've looked up my issue in FAQ
• I've searched for an already existing issues here
• I've tried running master-labeled docker image and the issue still persists there
• I'm running a supported version of the application which is listed here

Describe the bug (actual behavior)

when kafka-ui can't access the remote broker, it waits for a long time (this should also have timeout).
Meanwhile in the UI you see the loader in the topics page.

In the network tab I can see long request:

http://server/api/clusters/<cluster>/topics?page=1&perPage=25&showInternal=true

At some point it fails with 504, but the loader is still shown on the UI

Expected behavior

Loader should be removed and the error message should be shown

Your installation details

56fa824

Steps to reproduce

1. make sure kafka ui can't access remote broker.
2. visit topics page in that cluster

Screenshots

No response

Logs

no logs in the app output

Additional context

No response

[Haarolean]

it waits for a long time (this should also have timeout).

it does have one, it's admin client timeout.

[Haarolean]

TODO: Handle 504s from the backend properly