feat: add branch-based versioning for PR AMI builds

[jfroche]

Improvement of #1902 (reverted in #1905).

Manually create unique Postgres version names in branch often leads to version conflicts with the base branch versions. These conflicts force developers to deal with manual conflict resolution and unnecessary rebuilds.

To address this, this change implement automatic branch-based versioning for AMI builds triggered via workflow_dispatch on non-develop and non-release branches. The branch name is sanitized and appended to the Postgres version string.

We also publish pg_upgrade scripts and bin flake version right after the AMI release workflow completes.

Example: Branch 'multi-version-ext/pg-partman' produces postgres version 'multi-version-ext-pg-partman'