fix #508 by checking for `.Values.nextcloud.existingSecret.tokenKey`

Description of the change

Fix setting NEXTCLOUD_AUTH_TOKEN env var for metrics deployment by ensuring we check for .Values.nextcloud.existingSecret.tokenKey. Also sets .Values.nextcloud.existingSecret.tokenKey to default to '' which shouldn't be a breaking change, considering it was broken before.

Benefits

Now users can actually use the nextcloud.existingSecret.tokenKey feature.

Possible drawbacks

users will need to remember to set nextcloud.existingSecret.tokenKey

Applicable issues

fixes #508

Additional information

Fix originally described here: https://github.com/nextcloud/helm/issues/508#issuecomment-2249855493

Checklist

[x] I have read the CONTRIBUTING.md doc.
[x] DCO has been signed off on the commit.
[x] Chart version bumped in Chart.yaml according to semver.
[x] (optional) Parameters are documented in the README.md

nextcloud / helm