Add option to include exclude alerts via their labels

[martialblog]

Fixes #113

See #111

[martialblog]

@gianmarco-mameli @mattttv

This PR introduces --include-label and --exclude-label flags for alerts. Feel free to test this and give feedback.

[gianmarco-mameli]

Hi @martialblog thank you, I'll give a try and I get back to you with some results

[mattttv]

hello @martialblog. thanks for your efforts - awesome!
I tested this in a cluster 4.19.10 without any user prometheus (because the filter in openshift metrics is somewhat limited and gives wrong amounts of checks because it mixes user with core)
i checked with one --include-label severity=MYSEVERITYwhere severity was critical,info,warning,none and everything worked great! nice!
then I combined two params --include-label severity=none --include-label severity=info and it looks like only the last parameter is used - so there is a problem with the logic

check_prometheus alert --include-label severity=none
yields 1 alert
check_prometheus alert --include-label severity=info
yields 23 alerts
check_prometheus alert --include-label severity=none --include-label severity=info
yields 23 alerts
check_prometheus alert --include-label severity=info --include-label severity=none
yields 1 alerts

single exclude-label also seem to work but multiple params seem only to take the first one into account (so the other way round than with include).

Cheers,
Matt