Init NetBox Operator Helm chart

[LeoColomb]

This PR implements a Helm chart for the NetBox Operator.

Resolves netbox-community/netbox-operator#105

Tasks

Beta Give feedback

1. Templates & Rendering
2. Integration tests
3. READMEs and docs

[LeoColomb]

Thanks for your review, @jstudler!
Indeed, just switched to an empty default so it can use the upstream value.

While I think I'm mostly done with the chart, I struggle to set up a correct CI environment.
Having a NetBox automatically configured with restorationHashFieldName custom field seems difficult to automate.
Do you have an instance available for test somewhere? If not, do you have a way to automate?