Remove extra docker volumes and extra associated configurations

[KevinMind]

Fixes: mozilla/addons#15066

Description

• Updated docker-compose.yml to simplify volume mounts by using the current directory for all services.
• Removed HOST_MOUNT and HOST_MOUNT_SOURCE environment variables from settings and entrypoint scripts, streamlining the configuration for local and production environments.
• Refactored setup.py to eliminate the get_olympia_mount function, replacing it with a more straightforward approach to determine the Docker target.
• Adjusted GitHub Actions workflows to remove references to the obsolete mount input, ensuring cleaner CI/CD processes.
• Enhanced test cases to reflect changes in Docker configuration and environment variable handling.

Context

This patch drastically simplifies how we mount files into docker containers:

• there is a single bind mount from the root repo into any and all containers that need files.
• every container expects to find files at /data/olympia/**
• the mount is always on, we preemptively configure the host file system to reflect the desired container state so we can straight mount the files when running the containers

Warning

This means that the state of your host and the state of containers is 100% matching. so running remote built production containers require first checking out the commit that image was built on. This can be done manually right now and could be automated in the future.

Testing

Running make up in prod or dev mode will result in the exact same state where the root repo directory is mounted into /data/olympia no matter what.

Checklist

• Add #ISSUENUM at the top of your PR to an existing open issue in the mozilla/addons repository.
• Successfully verified the change locally.
• The change is covered by automated tests, or otherwise indicated why doing so is unnecessary/impossible.
• Add before and after screenshots (Only for changes that impact the UI).
• Add or update relevant docs reflecting the changes made.