[NextJS] Local docker setup

[ChristopherChudzicki]

What are the relevant tickets?

For https://github.com/mitodl/hq/issues/5396 [the local development half]

Description (What does it do?)

Enables running NextJS frontend in docker locally.

How can this be tested?

On this branch:

1. Stop your docker containers. Run docker compose up
2. Run docker compose logs watch --follow --tail=500 in a new terminal to see the watch logs. You should see NextJS logs
3. Visit http://open.odl.local:8062/ ... you should see the site. One way you will know it's the NextJS site—besides the docker logs—is to look at the initial HTML document, which will not be empty (as it is on main):
   
4. Ensure there are no CORS or CSRF errors. (There will be some other errors in the console we still need to deal with.)

[ChristopherChudzicki]

@jonkafton Opinion: We shouldn't use a frontends/main/.env.example file.

I know NextJS will use a .env file, but

• the majority of the time, developers are using docker to run the app. Docker has the env vars in the environment, populated from env/shared.env, etc
• If you're running outside of docker, let's use the same env files—env/shared.env, env/frontend.env, etc.
  • They can be loaded into shell automatically via some other tool, your choice. I use https://direnv.net/ for this (which @rhysyngsun suggested) and have been very happy with it.

[jonkafton]

Yes, agree - all of these ended up being public, so can live in the committed env files.

[jonkafton]

We'll hopefully end up addressing the API from within a local network (so the server isn't making API requests over the internet), though for now this holds true