* Add support for PostgreSQL 16

This requires Alpine 3.19

* Drop support for PostgreSQL 11

Version 11 has reached end-of-life (EOL)
https://www.postgresql.org/support/versioning/

* Install aws-cli via apk instead of pip3

This removes python3 and py3-pip as explicit dependencies.
Python is still installed as a derived dependency.

This fixes building on Alpine 3.19

* Add ARM64 builds

* Move to a go-cron fork with arm64 support

* Use TARGETARCH directly in the script

* Use buildkit for docker build in readme

Added BACKUP_KEEP_DAYS option.