Auto-generate helm values in README.md

[danielhoherd]

This is a first crack at auto-generating the helm values in the README.md, as described briefly in #206. I'm not sure if this is a great idea, so I haven't finished this. I wanted to open this up to discussion before making any more progress.

One thing I'm not happy about is how the table contents are not rendered in an ascii readable way. I experimented with auto-formatting using prettier, but having both helm-docs and prettier modifying the file led to an always-fail scenario.

Another problem is that our values go so deep, the resulting table has horizontal scrolling that hides all but the left-most column. See https://github.com/astronomer/airflow-chart/blob/7384359163/README.md

[kaxil]

I like the approach, I pushed 5210691 to reduce the width (horizontal scrolling):

WDYT now @danielhoherd : https://github.com/astronomer/airflow-chart/blob/5210691162b5946d69c66362cd125868194d7654/README.md#values