fix(helm): Add missing extraConfigs template volume mapping and fix type error on template.

[danielewood]

SUMMARY

Two parts:

1. superset-extra-config configMap was not attached to the deployment container
2. You cannot use "." inside a range with tpl. Instead "$" for global context can be used.
   • Reference Tpl funcion does not work in range helm/helm#5979

I also cleaned up the template slightly to result in the desired formatting no matter the input whitespace, thanks to @Yann-J for the feedback.

TEST PLAN

1. Attempt to use extraConfigs:

test_config=$(cat<<'EOF'
extraConfigs:
  test.yaml: |
    test data
EOF
)
helm template deploytest superset -f - <<<"${test_config}"

2. See error:

Error: template: superset/templates/configmap-superset.yaml:30:16: executing "superset/templates/configmap-superset.yaml" at <.>: wrong type for value; expected chartutil.Values; got string

3. Apply this PR.
4. Attempt to use extraConfigs
5. Template builds configs, including volume maps

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