Assist in visualizing the PostgreSQL vacuum process

[phumpal]

Use sensu to aggregate vacuum metrics from the pg_stat_progress_vacuum view.

Per https://www.postgresql.org/docs/12/progress-reporting.html#VACUUM-PROGRESS-REPORTING

Pull Request Checklist

Is this in reference to an existing issue?

General

• [x] Update Changelog following the conventions laid out here

• [ ] Update README with any necessary configuration snippets

• [ ] Binstubs are created if needed

• [x] RuboCop passes

• [x] Existing tests pass

New Plugins

• [x] Tests

• [ ] Add the plugin to the README

• [ ] Does it have a complete header as outlined here

Purpose

Known Compatibility Issues

[phumpal]

I may need to wait a day or two to accumulate a nice chart for these but will circle back when I have test results.

[phumpal]

Example output

staging-postgres-test-1.postgresql.vacuum.test_db.pid 24186 1591329314
staging-postgres-test-1.postgresql.vacuum.test_db.relid 154544 1591329314
staging-postgres-test-1.postgresql.vacuum.test_db.phase 2 1591329314
staging-postgres-test-1.postgresql.vacuum.test_db.heap_blks_total 82308 1591329314
staging-postgres-test-1.postgresql.vacuum.test_db.heap_blks_scanned 82308 1591329314
staging-postgres-test-1.postgresql.vacuum.test_db.heap_blks_vacuumed 0 1591329314
staging-postgres-test-1.postgresql.vacuum.test_db.index_vacuum_count 0 1591329314
staging-postgres-test-1.postgresql.vacuum.test_db.max_dead_tuples 96218052 1591329314
staging-postgres-test-1.postgresql.vacuum.test_db.num_dead_tuples 85 1591329314

[phumpal]

PTAL

[phumpal]

Gentle ping @majormoses @jspaleta

[majormoses]

released: https://rubygems.org/gems/sensu-plugins-postgres/versions/4.1.0

[phumpal]

Awesome. Thanks again @majormoses !