Add more language support

[camerondurham]

Ideas on more languages to add:

• Go (very easy, we already have Go installed in the image)
• C (should be relatively easy, image already requires uses gcc)
• Ruby (honestly who uses this?)
• Rust
• Zig

See #82 for what files should be modified. Calling out in particular:

Backend

1. Server Dockerfile (for adding any dependencies required for the server image): https://github.com/camerondurham/runner/pull/82/files#diff-e3dc0276ffd991d263bbb04bce5d89d0773bb4069c96ef46282902681ec64ba3
2. language.go (for adding language config, how to compile (if it's compiled of course) and run): https://github.com/camerondurham/runner/pull/82/files#diff-3c34a65e1f5cf2827cbca5707c44a4301816d2c713a80ab9e868a6e221db08a3
   a. need to add language config
   b. add language to SupportedLanguages, SupportedLanguagesSet so server accepts new lang requests
3. Add new test cases in language_test.go as well

Frontend

1. set-code.js (for adding language starter code to the dropdown): https://github.com/camerondurham/runner/pull/82/files#diff-1d55dc40f31e290098a80b8785b23ffa804a4fbd7cc1f81aa95f08207cb6ff6e