fix(helm): Fix inconsistency for the chart appVersion and default image tag

[dnskr]

SUMMARY

There is an inconsistency between the chart appVersion value and default image tag, that was introduced in PR #26923.

File Chart.yaml declares 3.1.0 as default supported version to be deployed by the chart:

...
apiVersion: v2
appVersion: "3.1.0"
description: Apache Superset is a modern, enterprise-ready business intelligence web application
name: superset
...

It's also visible by the following command:

$ helm search repo superset
NAME                    CHART VERSION   APP VERSION     DESCRIPTION
superset/superset       0.12.2          3.1.0           Apache Superset is a modern, enterprise-ready b...

However, the chart uses latest image tag that may change over time:

$ helm show values superset/superset --jsonpath '{.image.tag}'
latest

As far as I know, it's a good practice for Helm charts to set explicit value to appVersion and use it as default version to be deployed. For example, Airflow, ArgoCD and other Helm charts use this approach.
The PR partially reverts PR #26923!

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