Update postgres to 13.16

[ChrisW-B]

Description

Updates postgres from 13.0 to 13.16. Currently, when starting BookWyrm with ./bw-dev up, the postgres step fails as http://apt.postgresql.org/pub/repos/apt no longer hosts repositories for Debian Buster, which instead uses Debian Bookworm and is still supported. The postgres docker also moved the location of its entrypoint, so the PR also updates docker-entrypoint.sh to /usr/local/bin/docker-entrypoint.sh

• Closes Production branch builds are broken due to postgres no longer serving buster repository #3439

What type of Pull Request is this?

• Bug Fix
• Enhancement
• Plumbing / Internals / Dependencies
• Refactor

Does this PR change settings or dependencies, or break something?

• This PR changes or adds default settings, configuration, or .env values
• This PR changes or adds dependencies
• This PR introduces other breaking changes

Details of breaking or configuration changes (if any of above checked)

Upgrades postgres from postgres:13.0 to postgres:13.16 (not breaking in my testing, but a configuration change nonetheless)

Documentation

• New or amended documentation will be required if this PR is merged
• I have created a matching pull request in the Documentation repository
• I intend to create a matching pull request in the Documentation repository after this PR is merged

Tests

• My changes do not need new tests
• All tests I have added are passing
• I have written tests but need help to make them pass
• I have not written tests and need help to write them