Maybe switch to local pool DbHandler strategy

Seeing a lot of busy_dist_port messages due to TCP connections between nodes being saturated or otherwise experiencing some packet loss or head-of-line blocking.

We should also reduce the number of hops to the database to reduce latency. -Just- need to share or acquire a global count of database connections.

• Poll pg_stat_activity and cache Supavisor connection count on an interval
• max pool size per node should be a function Node.list + 1 / sum of application_name filtered by pool_pid
• application_name of DbHandlers should be something like Supavisor Pool - #{pool_pid}
• Expire cache maybe 5 seconds?

Option 1

• "primary" node with manager
• need query rate per connection in manager
• manager should be able to dynamically change pool size and calibrate pool size on each node
• nodes with busier connections should have relatively more conns to the database