Add vacuum analysis queries & dashboard

[keithf4]

Add a new query file for doing more in-depth vacuum analysis.

See this blog post for details - http://dtrace.org/blogs/dap/2019/05/22/visualizing-postgresql-vacuum-progress/

Keep this as a separate file to allow it to be optional since it could potentially be very noisy. Recommend having monitoring query only target specific tables that can be set by user.

[keithf4]

Pulled from #294

Describe the enhancement you are proposing:

Would be nice to see a line chart graph in the PG details dashboard showing the number of autovac workers currently running as a percentage of the autovacuum_max_workers so you know if it needs raised/lowered.