libobs/frontend: Add callback for reconnection decision

[dsaedtler]

Description

Adds a callback for making reconnection decision.

Also reverts #11304

Motivation and Context

#11304 was necessary for #11452, but negatively impacted regular users as some servers would not accept a reconnection attempt after the default retry time (2 seconds), which resulted in some users seeing a warning message instead of automatic reconnection.

To restore the old behaviour, we instead add a new callback that makes it a decision by the output's creator on whether or not they want to allow a reconnect attempt.

In addition to a simple yes/no decision this also allows reconfiguring the output in the callback, allowing for a futrue rework of #11452 that does not rely on the somewhat ugly UI changes to hijack the regular disconnect logic and instead updates the output in-place before returning.

How Has This Been Tested?

Verified regular output still works fine. Will need more testing.

Types of changes

• Tweak (non-breaking change to improve existing functionality)
• Code cleanup (non-breaking change which makes code smaller or more readable)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[exeldro]

Documentation change is missing