Update umask before launching foundry if CONTAINER_UMASK is set

[eltariel]

🗣 Description

This change introduces an environment variable, ${CONTAINER_UMASK}, to control the umask of the node process. If this variable is set, launcher.sh passes it to the umask command before launching node.

💭 Motivation and context

This change makes it easier to manage shared assets between containers without needing them all run as the same user.

TODO: describe this better.

🧪 Testing

TODO: describe this better.

To check if umask is set:

• Start container using docker compose.
• Check logs for umask messages
• Run docker compose exec foundry find -L /proc -maxdepth 2 -name exe -samefile /usr/local/bin/node -print -execdir grep Umask status \; to check the umask of the foundry process - there should only be one match.
• Stop the container.

Repeat the check for at least these situations:

• CONTAINER_UMASK unset => no log, umask is 0022
• CONTAINER_UMASK=0002 => info message printed, umask is 0002
• CONTAINER_UMASK=(symbolic representation - TODO) => info message printed, umask matches
• CONTAINER_UMASK=oops => info message, warning message, umask is 0022. Container starts as normal.

✅ Pre-approval checklist

• [x] This PR has an informative and human-readable title.
• [x] Changes are limited to a single goal - eschew scope creep!
• [ ] All future TODOs are captured in issues, which are referenced in code comments.
• [ ] All relevant type-of-change labels have been added.
• [x] I have read the CONTRIBUTING document.
• [ ] These code changes follow cisagov code standards.
• [x] All relevant repo and/or project documentation has been updated to reflect the changes in this PR.
• [ ] Tests have been added and/or modified to cover the changes in this PR.
• [ ] All new and existing tests pass.

✅ Pre-merge checklist

• [ ] Revert dependencies to default branches.
• [ ] Finalize version.

✅ Post-merge checklist

• [ ] Add a tag or create a release.