Bug 1946490: Mount /tmp as tmpfs in containers with d2g

[Eijebong]

I'm not sure why docker doesn't do this by default but it sounds like a no-brainer to me. Some tasks might have some disk heavy things that could be done on a tmpfs and there's no way to mount one after the container has been created.

Part of Bug 1946490.

Note that this contains #7515 as I really didn't feel like updating all those test expectations manually, this PR is only about the last commit.

[Eijebong]

CC @hneiva

[petemoore]

CC @jcristau

[jcristau]

I think we should punt on this until after we've actually deployed d2g in fxci, since this is not a parity gap with docker-worker.

[petemoore]

I'll put back to DRAFT while we are punting, and then we can mark it ready for review again when we want to come back to it (just so it doesn't stay in our queue).