feat(helm): Evaluate configOverrides as templates

[Yann-J]

SUMMARY

This change will evaluate configOverrides as templates. This allows making those overrides dynamic and use input values from values.yaml which may not be easy to ingest as env variables. For instance:

configOverrides:
   reports: |
    WEBDRIVER_BASEURL = "http://{{ template "superset.fullname" . }}:{{ .Values.service.port }}/"

TEST PLAN

• Update your values.yaml with some values based on Helm values - see example above
• helm upgrade your chart release

ADDITIONAL INFORMATION

• Has associated issue:
• Changes UI
• Requires DB Migration.
• Confirm DB Migration upgrade and downgrade tested.
• Introduces new feature or API
• Removes existing feature or API

[Yann-J]

Hi there @craig-rueda just a quick ping on that last Helm-related PR from my side... This one was a bit of a leftover from the previous one on config overrides, and should be very safe to merge...