fix: update default values to account for postgresql existingSecret

[PatAKnight]

Description of the change

Adds two new functions that will be used to set the values at upstream.backstage.extraEnvVars.valueFrom.secretKeyRef.name and upstream.postgresql.primary.extraEnvVars.valueFrom.secretKeyRef.name. These functions will check if upstream.postgresql.auth.existingSecret is set and set the above values to this value. Otherwise it will set them to release-name-postgresql

Existing or Associated Issue(s)

• Setting existingSecret for PostgreSQL is not respected by our default values #138

Additional Information

I am setting this as a draft so that I can get it reviewed to ensure that this is the route that we wish to go.

Checklist

• Chart version bumped in Chart.yaml according to semver.
• Variables are documented in the values.yaml and added to the README.md. The pre-commit utility can be used to generate the necessary content. Use pre-commit run -a to apply changes.
• JSON Schema template updated and re-generated the raw schema via pre-commit hook.
• List tests pass for Chart using the Chart Testing tool and the ct lint command.

[tumido]

Just a suggestion for enhancement 🙂

[tumido]

Just a single comment, otherwise LGTM 🙂

[tumido]

I've left few suggestions inline... I think we should be consistent with upstream in value priority.

In addition to that, I've fixed the thing you've mentioned as broken in the upstream Backstage chart:

backstage/charts#154

[tumido]

I have 1 nit remaining. In addition to that, can you please rebase and bump the version once more? 🙂

[tumido]

/lgtm
/approve