fix(docker): set HOME environment variable explicitly in Dockerfile

[gustavovalverde]

Motivation

The HOME environment variable was defaulting to /root when the container started, causing cache directories to be incorrectly set up under /root/.cache/zebra instead of /home/zebra/.cache/zebra

This happens as the user running the entrypoint.sh (before using gosu) is the root user

The initial intention was not to override the default linux $HOME, but in this controlled environment there's no actual benefit in not doing so.

Solution

• This explicit setting ensures the HOME environment variable is correctly set to the zebra user's home directory.

Tests

• Carefully check the unit tests:
  • Test default-conf in Docker
  • Test testnet-conf in Docker
  • Test custom-conf in Docker

As their exit code is not being handled correctly

Follow-up Work

• Docker configuration tests should exit with the appropriate exit code when this kind of scenarios happen

PR Checklist

• The PR name is suitable for the release notes.
• The solution is tested.
• The documentation is up to date.
• The PR has a priority label.
• If the PR shouldn't be in the release notes, it has the
  C-exclude-from-changelog label.