Update git-sync with newer version

[danielhoherd]

Official Helm Chart version

1.7.0 (latest released)

What happened

The current git-sync image that is used is coming up on one year old. It is also using the deprecated --wait arg.

What you think should happen instead

In order to stay current, we should update git-sync from 3.4.0 to 3.6.1.

Are you willing to submit PR?

• Yes I am willing to submit a PR!

Code of Conduct

• I agree to follow this project's Code of Conduct

[danielhoherd]

One problem I see here is that the --wait flag, which exists in 3.4.0 but is deprecated in 3.6.1, has an env var GIT_SYNC_WAIT and is defined in helm as .Values.dags.gitSync.wait. We would want to change that to --period with GIT_SYNC_PERIOD as its env var, and .Values.dags.gitSync.wait as its helm value. This would break existing installations. Should we have a deprecation period where we support both the deprecated --wait and --period, which correlates with how git-sync is doing it? If so, is there a standard way that Airflow does that, or should I just leave a comment saying that the option should be removed when it is removed from the git-sync command?

Relevant help text (from https://github.com/kubernetes/git-sync#manual):

    --period <duration>, $GIT_SYNC_PERIOD
            How long to wait between sync attempts.  This must be at least
            10ms.  This flag obsoletes --wait, but if --wait is specified, it
            will take precedence.  If not specified, this defaults to 10
            seconds ("10s").