[bitnami/discourse] Bump subcharts and common helpers

[joancafom]

Signed-off-by: joancafom [email protected]

Description of the change

This PR updates PostgreSQL and Redis subchart to the new major versions. The former includes breaking changes that affect this chart. More info at #3021 and #3658 respectively.

Also, took the chance to implement some standardizations using bitnami/common library chart, such as: password validation on upgrade, simplification of _helper.tpl & use of standard labels (non-breaking change, this chart already included them but now using bitnami/common approach)

Benefits

Standardization, up-to-date subcomponents

Possible drawbacks

Breaking backwards compatibility

Applicable issues

NA

Additional information

Checklist

• Chart version bumped in Chart.yaml according to semver.
• Variables are documented in the README.md
• Title of the PR starts with chart name (e.g. [bitnami/chart])
• If the chart contains a values-production.yaml apart from values.yaml, ensure that you implement the changes in both files

⚠️ Keep in mind that if you want to make changes to the kubeapps chart, please implement them in the kubeapps repository. This is only a synchronized mirror.

[miguelaeh]

Thank you very much for the PR!!!
Please take a look at my comments.

[miguelaeh]

I left some comments similar to the previous one

[miguelaeh]

LGTM!