feat: build PgBouncer images with bake

[NiccoloFei]

Refactor this project to use the same bake process implemented by the other CNPG repositories.

What's been done:

• New tags (in total 3 now) to contain both the distro and the timestamp (e.g 1.24.1, 1.24.1-trixie, 1.24.1-202510141550-trixie)
• Provide SBOM and proper build annotations/labels for the image (because of this, the legacy packages.txt method of tracking files has been removed).
• Update the Debian base image to use trixie
• Removed several unneeded packages from the image, which reduced the images size from ~600MB to ~200MB
• Use renovate to update GH actions and the base debian image
• Updated GH workflows (build.yml & update.yml) accordingly

Important:
The image has been updated to use the pgbouncer package from Debian instead of building from source.
The pgbouncer package is built using c-ares as DNS backed, while our current images are using libevent (evdns2).

Closes #60 #55

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