Docker compose setup for locally testing the whole OCaml-CI stack

[benmandrew]

The tested stack currently involves:

• service, the OCaml-CI service for GitHub.
• web, the front-end web interface.
• scheduler, for scheduling jobs.
• worker, a single Docker-based worker. I'm on Mac, and the default rsync didn't work first time so I just set it to Docker.
• caddy, for reverse proxy stuff (unsure if necessary).

Rebased on top of the contents of #883.

To run

1. In docker-compose.yml, change the file paths under the secrets label to point to your own relevant local files.

2. scheduler, worker and caddy pull pre-built images from Docker Hub; service and web must be built as local images by running:

   docker build -t ocaml-ci-service -f Dockerfile .
   docker build -t ocaml-ci-web -f Dockerfile.web .

3. Create a file at /etc/caddy/Caddyfile containing:

   
   https://localhost:8100 {
   reverse_proxy service:8080
   }

https://localhost { reverse_proxy web:8090 }

4. Run `docker compose up`.

[benmandrew]

On my machine web is currently failing with:

Failed to connect to backend: Failure("Failed: Network connection for tcp:service:8102 failed:\n  Unix.Unix_error(Unix.ECONNREFUSED, \"connect\", \"\")")

[benmandrew]

Two new containers have been added:

1. solver-worker for doing local solves
2. scheduler-cap for generating the capability file needed by service to submit jobs to scheduler

[benmandrew]

The docker compose setup does not include a GitLab service container. The documentation for running the GitLab service locally has been moved to its own file doc/gitlab-dev.md due to doc/dev.md now being about running the docker compose rather than setting up each component manually, as it was before. There may be a better solution for this.

[moyodiallo]

Is this inspired from docs-ci https://github.com/ocurrent/ocaml-docs-ci/blob/main/docker-compose.yml ? Otherwise you could find some useful thing there too.