fix: postgres data mountpoint

[mxyng]

Summary

Using the data mountpoint directly causes problems for postgres in certain scenario where the directly may not initialize empty. Instead, use a subdirectory under the mountpoint to store the actual data.

• Add migration to move data previously stored in the mountpoint to the subdirectory (/var/lib/postgresql/data -> /var/lib/postgresql/data/pgdata)
• Fix postgres health checks to use the right user and database name
• Bump appVersion to 0.16.1, chart version to 0.20.5

Testing Migration

• Install Infra locally with chart 0.20.4
• Load some data (users, groups)
• Upgrade chart
• Verify data still exists

Testing AWS

• Install Infra with chart 0.20.4.
• Postgres pod goes into crash loop
• Install updated chart
• No crash loop

Related Issues

Resolves #3124
Resolves #3555