Change proposal for GitHub Action runs

[swiffer]

This is a proposal for changing GitHub Actions / Workflows.

I'm happy to gather any feedback before taking action / working on the GitHub Action setup.

Testsuite

1. Matrix test with lowest / locked / highest versions
   (Verifying our promise of keeping support for last 3 versions and being able to test on new versions early)
   • lowest: Elixir 1.17.3-otp26, Postgres 16.7-bookworm [allowed-to-fail ?]
   • locked: Elixir 1.19.5-otp26, Postgres 18-trixie
   • highest: Elixir 1.19.5-otp28, Postgres 18-trixie [allowed-to-fail ?]

Docker Images on GHCR

1. Run GitHub Registry Workflows to build Docker Images for edge (main branch) as well
   (Allows using caches for Docker image builds (Grafana+Teslamate) on GitHub Action runs for newly created PRs)

2. Use Registry Cache for Grafana image
   (With Grafana being a single stage build the inline cache works well, gha cache backend is branch specific means low cache hit rate)

   • cache-from: type:registry,ref=teslamate/grafana:pr-XXXX
   • cache-from: type:registry,ref=teslamate/grafana:edge (requires 2.)
   • cache-to: type=inline,mode=min

3. Change GitHub Action Image for ARM to ubuntu-24.04-arm
   (ARM is supported natively on GitHub now - switching to reduce complexity going forward)

4. Move Multi-Stage Build-Cache Images for TeslaMate to a different Image (e.g. teslamate/buildcache)
   (Teslamate Buildcaches are currently stored in /teslamate causing a lot of tagged versions)

5. Ensure Build-Caches of merged PRs are deleted (requires 4.)
   (When closing / merging a PR the corresponding Docker Tags are removed - this isn't working for buildcache tags currently - having a separate image and revised naming this can be archived as well (e.g. teslamate/buildcache:pr-4567-amd64)

6. Reuse Caches of Edge when building TeslaMate images for PRs (requires 2.)

7. One-Time Cleanup of tagged images
   (Grafana & TeslaMate images on GitHub are flooded with outdated tagged images (buildcaches / closed PRs - once 1-6 are done, do a one-time cleanup)