[sssd PR#5223][synchronized] [wip] Add .clang-format

[pbrezina]

URL: https://github.com/SSSD/sssd/pull/5223
Author: pbrezina
 Title: #5223: [wip] Add .clang-format
Action: synchronized

To pull the PR as Git branch:
git remote add ghsssd https://github.com/SSSD/sssd
git fetch ghsssd pull/5223/head:pr5223
git checkout pr5223