Optimize Postgres storage concurrent connection count

[khawarizmus]

Context:

The official documentation recommends 100 to 200 concurrent connections per container.. There is an undocumented configuration that allows us to increase the number of concurrent connections per Powersync instance

api:
  parameters:
    max_concurrent_connections: 1000

The team has made a 10-5X improvements on the number of concurrent connections possible for Powersync useing MongoDB as a storage since then.

See:

• Optimize write checkpoints lookups Optimize write checkpoints lookups #230
• Cache parameter queries and buckets Cache parameter queries and buckets #200

For more context see this Discord thread

This is issue is to track similar improvement but for Postgres. It is also aims to help the team do a better triage.