Superset repackaging as beta release/helm packages build, test, lint, helm-docs, publication

[idirze]

This chart is a wrapper (or a meta chart) above the original official superset chart and references it as a subchart dependency to provide overrides and enrichment for the existing default values.

Objectively, the chart provides the following features:

1. An implementation for a custom Oauth2/OpenId providers which includes keycloak and Dex IdP.
2. Externalizes the secrets into a specific okdp secrets for the database, Oauth2, redis and superset related credentials.
3. Provides high level configuration for superset deployment by overriding the default superset original values.
4. Provides an ability to add additional future components (like monitoring) or replace existing ones (like original subcharts for redis and postgresql database).
5. Seamless configuration and deployment.

The PR also automate the Build, lint, test, helm-docs generation for all helm charts and publish the packages into Github Releases. An index.yaml is automatically updated in the branch gh-pages which reference the published releases.