More documentation: data modeling for distributed systems, pgBouncer, and others

[ozgune]

More documentation: more on data modeling for distributed systems, how our users set up pgBouncer, and items that were cut out from docs v1

[marcocitus]

Some pointers: https://docs.microsoft.com/en-us/azure/postgresql/hyperscale/concepts-connection-pool https://docs.citusdata.com/