[DevOps] - Self-host github build runners to validate buildroot builds

Current Features

Right now, the reviewer of a PR has to wait the hour or so for the specific defconfig to build to validate the code does not break anything at compile time. Technically all 3 defconfigs should be built, which takes up to 4 hours right now.

Desired Additional Features

Github free minutes + free storage is too constrained for buildroot. They do hoever have self-hosted runners that integrate into the web ui just like the github-hosted ones. We should harness this configuration, along with the recently added #63, to reproduce builds both for CI checks and for creation of release binaries once releases are made as competition approaches.

Technically this could be done with a raspberrry pi plugged into a USB HDD of 128+ gb, along with a heatsink and/or aggressive temperature throttling on the pi. This would wear on the pi quick, so def we should use one of the old pi 3s.

Screenshots (as needed)

No response

Start by reviewing the repository's existing GitHub Actions configuration and the changes referenced in issue #63. Define a self-hosted Raspberry Pi runner that can reproduce all three defconfig builds for CI and produce release binaries, then verify the workflow in GitHub's checks and release process.