Add blacklist of consumer groups

[graphex]

As mentioned in #4 a consumer group name blacklist in addition to the whitelist would also be useful for ignoring console consumers, for example.

[seglo]

I've thought about this some more and I agree that exposing a blacklist for consumer groups (and all the other features that currently have whitelists: topics, metrics) would be useful.

[edrzmr]

@graphex @seglo I will do the job, would you assign to me?

[seglo]

@drrzmr Done. Thanks for volunteering!

[pimpelsang]

Also interested in this feature!

[Manicben]

Apologies for the spam, had forgotten about my work machine's git setup being different.

I've gone ahead and implemented the above, as it would make our Prometheus instance and storage much happier if consumer groups with uuids were filtered out from the get go.