feat: Add dockerfile for easier selfhosting.

[SelfhostedPro]

Hey, think it would be useful to add a Dockerfile for selfhosting. If there's a better location for them, please let me know. I can also make a PR for a github action to build and push this image.

I'm just using a basic nginx:stable-alpine image and a nginx.conf that serves /app inside of the container. If this isn't needed, you want documentation added for easy building/launching, or those actions please @ me.

To test it out run:

docker build -t test .
docker run -d -p 8080:8080 test

Then it should be accessible at port 8080 in your browser on whatever machine you're running it on or at http://localhost:8080.