Cleanup/add gitlab exporters

[Sticksman]

This adds most of the diagonistic queries found in the gitlab queries.yaml: https://gitlab.com/gitlab-cookbooks/gitlab-exporters/-/blob/master/templates/postgres_exporter/queries.yaml.erb#L866

Several are difficult to write tests for:

• pg_xid has an Nan comparison that can't be made, so had to special case that test
• the summary queries use some pretty complex regexes that are difficult to sanitize, which means tests were nearly impossible to write. I checked on a postgres db and they seemed to work alright.

[sysadmind]

I know this is still a draft and changes may still come. That said I took a brief look and I have 2 notes.

1. All of these new collectors are enabled by default. I'm not sure that every user would appreciate that behavior out of the box. The more queries that run out of the box, the higher the overhead of running this collector.
2. I don't understand the term marginalia or why it is used.

[SuperQ]

+1, we should be careful about what new collectors we enable by default.

[Sticksman]

Disabled everything by default and renamed marginalia (yeah I was kind of unclear on this term as well, I think summary was the best way I could read it as)

[Sticksman]

Will require #823

[igorwwwwwwwwwwwwwwwwwwww]

I don't understand the term marginalia or why it is used.

It's from the marginalia gem.

[Sticksman]

@sysadmind @SuperQ this is ready to go

[SuperQ]

Good so far. While we're importing these features, we should cleanup some best practices issues so we don't have to deal with them later.

[SuperQ]

Honestly, I would prefer to break this up into a few PRs. Doing this all as one big PR is hard to review.

[Sticksman]

I’ll work on splitting it up today

[sysadmind]

+1 I much prefer small PRs. Much easier to review. I would suggest one PR per "collector"

[Sticksman]

Closing for now