Update builds and metadata tooling

[AbstractUmbra]

Description

Update the repository and build stages to use PDM over Poetry. This allows for sleeker builds as well as multi-stage docker image support (resulting in a smaller final image).

Also move the usage of .env to use docker secrets instead. Env variables can leak into the final image, and can be read by consumers.
This doesn't apply to use due to the final image being untouchable outside of deployment staff, but it's best to follow best practices.

Checklist

• If code changes were made then they have been tested.
  • I have updated the documentation to reflect the changes.
  • I have updated the changelog with a quick recap of my changes.
• This PR fixes an issue.
• This PR adds something new (e.g. new method or parameters).
• This PR is a breaking change (e.g. methods or parameters removed/renamed)
• This PR is not a code change (e.g. documentation, README, ...)
• I have read and agree to the Developer Certificate of Origin for this contribution