IBS is not warning if there's an attempt to enable the maintenance channels in a maintenance incident with a release request open

[deneb-alpha]

Is your feature request related to a problem? Please describe.
the SUSE maintenance workflows is using channel files and patchinfo for defining to which products release a binary

As reported in openSUSE/osc#926, currently IBS doesn't have any validation in place for avoiding to perform the enablechannels command when the given maintenance incident has a release request open AND NOT in a final state.

Please, see also the full details of the issue reported in openSUSE/osc#926

Describe the solution you'd like
If the given incident has a release request open that isn't accepted revoked or declined, IBS should warn the user trying to issue the command and prevent to have the channels enabled.

Please, note that this feature should be valid only when a release request is in state review.

Describe alternatives you've considered
Implement internal validation on the maintsec-tools for preventing to issue the enablechannels command (see internal issue. this solution doesn't prevent a maintenance/security engineer to directly issue the osc command for enabling a channel.

Additional context
This is a follow-up from openSUSE/osc#926 where the advise was to report the problem on OBS and not on osc.