chore(helm): Split service templates into separate files

[dnskr]

SUMMARY

The PR splits Service resource definitions into separate files according to Helm Best Practices Guide:

• Each resource definition should be in its own template file.

Also service-account.yaml renamed to serviceaccount.yaml according to:

• Template file names should use dashed notation (my-example-configmap.yaml), not camelcase.

The PR does not change any functionality of the chart.

TESTING INSTRUCTIONS

The following command creates superset, superset-flower and superset-ws services.

helm template superset helm/superset --set supersetCeleryFlower.enabled=true --set supersetWebsockets.enabled=true

ADDITIONAL INFORMATION

• Has associated issue:
• Required feature flags:
• Changes UI
• Includes DB Migration (follow approval process in SIP-59)
  • Migration is atomic, supports rollback & is backwards-compatible
  • Confirm DB migration upgrade and downgrade tested
  • Runtime estimates and downtime expectations provided
• Introduces new feature or API
• Removes existing feature or API

[dnskr]

@craig-rueda Could you please have a look the PR?