ENH: harvest outage info for IRSA

E.g. today I run into TAP timeouts, which are part of the overall network issues at server side. We do have a banner for this though, so it maybe useful to harvest that info and provide to the python users, too.

Start by examining the IRSA and TAP query entry points and identify where the server-side outage banner information is available. Determine how that information should be harvested and presented to Python users, then define tests covering outage and normal-service responses; the issue names no specific files or tests.

Written by the indexing model from the issue text.