docs(alpha): add description

feat: support postgresql 18 as it's now available in Cloud SQL

fix: Point to nais doc about how to test the new instance after setup

fix: place aivenapp secret in correct field

feat(alpha): register apply, opensearch and valkey subcommands

build: remove unused variable

build: try base16

build: remove outdated livecheck

build: try different approach

build: fail if no files are uploaded