Closes #17051: Introduce the ISOLATED_DEPLOYMENT config parameter

[jeremystretch]

Fixes: #17051

• Introduce the ISOLATED_DEPLOYMENT config parameter
• Disable the following functionality when True:
  • Automatic release checks (housekeeping task)
  • Census reporting
  • Plugins catalog integration
  • External footer links

[arthanson]

ISOLATED_NETWORK ?

[m2martin]

I think it is worth to differentiate between the origin of requests. Some requests may originate from Netbox itself (e.g. release checks) which may fail due to isolation, others are originated from clients like the footer links which can be functional as the client is able to reach external ressources.

[jeremystretch]

@m2martin yeah that's a good point. I'm going to revert the footer link changes as those are client-facing.

[trrunde]

what about the rss feed on the default frontpage? I just installed netbox on a labserver where I use proxy to reach internet, the domainname where not allowed, so rss feed timed out making the front page slow to load. If its an airgapped installation the rss feed widget should be removed.