feat: Update git-sync to v4.4.0

[lostkamp]

What issues does your PR fix?

• Airflow git-sync is not working #885

What does your PR do?

Updates git-sync image to v4.4.0 and adapts the env variables accordingly.

The changes are backwards-compatible with the exception that the --branch and --rev flags have been merged to the new --ref flag. This implies that .Values.dags.gitSync.branch and .Values.dags.gitSync.revision should also be merged. I have implemented it like that following this table.

In the docs examples I have used the branch name as the revision, because I thought people would most likely want to specify a branch instead of "HEAD" or so and they might be confused if they don't see a way to do that.

The other option would be to not merge the values and rely on:

For backwards compatibility, git-sync will still accept the old flags and try to set --ref from them.

Checklist

For all Pull Requests

• Commits are signed off
• Commits have semantic messages
• Documentation updated
• Passes ct linting

For releasing ONLY

• Chart.yaml version bumped
• CHANGELOG.md updated