Respect umask

[dholth]

Description

This extends tarfile to apply umask (before ever creating the file with tar's default chown).

This should work if the program does not change its own umask. It is probably necessary to check umask with a global lock such as the one used by module level globals in the import system for thread safety.

Resolves https://github.com/conda/conda/issues/12829

[jezdez]

@awwad Do you have opinions on the way this was solved?

[dholth]

Does this affect the umask on implictly-created directories? (When we see an a/b/c/d.pywithout seeing directory entries for a/b/c in the tarfile?)