feat: Publish docker

[AverageHelper]

We might as well publish our own Docker image. Would make deployment much easier if a host could simply write ghcr.io/byu-cs-discord/csbot in a compose.yml file, without having to clone and build directly.

New Docker deploy flow:

• Every push to our main branch goes to an image tag called main
• Every new SemVer repo tag goes to an image tag called x.x.x, x.x, x, and latest
• latest is equivalent to the newest SemVer tag, while main is equivalent to the main branch
• Latest SemVer image can be pulled from ghcr.io/byu-cs-discord/csbot:latest
• We might additionally publish to our Codeberg mirror the same way, once I know this proof-of-concept works and I figure out how to matrix the secret key

Startup time is a bit slow during command deployment, but we can speed that up later with a smarter deployment solution (one that edits existing commands rather than strict redeploying, which I think would fix the issue with command permissions resetting each time).

Note also that we run database migrations on startup, too.

[AverageHelper]

Ok I think it's done now lol. Pending new reviews

[JstnMcBrd]

Excited to see this work when we release v0.13.0!

[AverageHelper]

Looks like the package was marked private lol, but now that's fixed and I've confirmed that the ghcr.io/byu-cs-discord/csbot:main image works! Once #165 merges then we should have semver tags and :latest as well!!

EDIT: Well something went wrong idk what lol