DEV-1385 expose prometheus metrics for catalog indexing

[moseshll]

• Add push_metrics to services.
• See README for ENV variables of interest.
• Add support for checking the pushgateway for metrics in the appropriate indexer tests.
• Add a postflight method for the indexer command, all it does right now is finalize the pushgateway job.
• Randomly TIDY the Gemfile and docker-compose with some list alphabetization.

As mentioned in a ht_tanka PR, JOB_NAME is set to index_catalog in this branch but for consistency should be set to catalog_indexing, I think?

[coveralls]

coverage: 92.552% (+0.004%) from 92.548%
when pulling c4941bd on DEV-1385_prometheus_metrics
into 01164c0 on main.

[aelkiss]

This all seems pleasantly straightforward especially in terms of the integration with each_record.

I'd be a bit inclined to default JOB_NAME to include the specific cictl subcommand being used -- the scenario I'm thinking about is wanting to ensure that ad-hoc runs don't stomp on or confuse the metrics from any more regular run.

[moseshll]

@aelkiss Requesting a quick final once-over because I moved some things around to get at the cictl ... command via Thor current_command_chain. It de-clutters Services a little so I reckon that is okay.

[aelkiss]

All makes sense to me. We'll give it a try in the testing workflow.