Postgres connection pooling not working

## The problem
Issue temporalio/temporal#4975 (closed, 13 comments): ## Expected Behavior
Connections rarely getting opened

## Actual Behavior
50% of all CPU load (4 cores) just from opening new connections

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## Steps to Reproduce the Problem

  1. cluster with 2k shards (I assume that's the culprit)
  1. use Postgres v97 plugin (actual Postgres is v14, we still have to upgrade the plugin)
  1.

## Specifications

  - Version: v1.20
  - Platform: Linux, AWS, EKS

## What fixed it
[tdeebswihart (contributor)]: The CPU/GC load from constant connection and TLS cert recreation comes from sqlx pool defaults (max 2 idle conns, unbounded pool). Set persistence.datastores.*.sql.maxConns and maxIdleConns explicitly. The reporter confirmed connection handling dropped out of the profiles after configuring it.