[TASK] Add a code of coduct document

Having a CODE_OF_CONDUCT.md document that links to the TYPO3 code
of conduct provides users who view the project source on GitLab
easy, direct access to the full text.
2 jobs for feature/coc in 3 minutes and 33 seconds (queued for 5 seconds)
Name Stage Failure
failed
Get dump for Content Master Maintenance
# demo01.typo3server.ch:22 SSH-2.0-OpenSSH_7.9p1 Debian-10+deb10u2
# demo01.typo3server.ch:22 SSH-2.0-OpenSSH_7.9p1 Debian-10+deb10u2
# demo01.typo3server.ch:22 SSH-2.0-OpenSSH_7.9p1 Debian-10+deb10u2
$ chmod 644 ~/.ssh/known_hosts
$ mkdir dump
$ ssh demo-content@demo01.typo3server.ch "php ./content.demo.typo3.org/current/bin/typo3cms database:export -c Default -e 'cache_*' -e '[bf]e_sessions' -e 'be_users' -e 'sys_log' -e 'sys_history' -e 'sys_refindex' | gzip -9 -c" > ./dump/dump.sql.gz
ssh: connect to host demo01.typo3server.ch port 22: Address not available
Cleaning up project directory and file based variables
ERROR: Job failed: exit code 1