zephyr/docker-build.sh: match UID with 'adduser' instead of 'chgrp -R'
This fixes SOF version.cmake which was just broken by a recent git
security update and started to fail like this:
```
-- SOF version.cmake starting at 2022-04-25T18:14:56Z UTC
-- /workdir/zephyr/.. is at git commit with parent(s):
fatal: unsafe repository ('/workdir' is owned by someone else)
To add an exception for this directory, call:
chgrp -R was always an ugly hack because it was messing with
(persistent) file permissions on the host, outside the container. This
new adduser solution is unfortunately much more code but it does not
leak any side effect outside the container.
Do not fix scripts/docker-run.sh yet because there is still no UID
mismatch between Github Actions and the SOF container (they're both
1001) but add a warning + TODO.
Signed-off-by: Marc Herbert <email address hidden>
(cherry picked from commit d09844ab98cc0f03681d2edbc0395a4f3e1a17ee)
