mgr/dashboard: user accounts enhancements

mgr/dashboard: user accounts enhancements

fixes: https://tracker.ceph.com/issues/72072

PR covers:
1) Displaying account name instead of account id in bucket list page & bucket edit form for account owned buckets
2) non-root account user can now be assigned with managed policies with which they can perform operations
3) The root user indication shifted next to username in users list rather than on Account Name with a new icon.

Signed-off-by: Naman Munet <naman.munet@ibm.com>