[bitnami/harbor] Fix REGISTRY_HTTP_SECRET creation when not using an existing secret

[uivraeus]

Description of the change

Ensure that REGISTRY_HTTP_SECRET can be assigned when there is no existing Secret with a value for it.

The fix is to let the temporary variable used for a potentially existing secret value default to an empty string. This follows the implementation strategy applied in "core-secret-envvars.yaml"

Benefits

Possible to control the value of REGISTRY_HTTP_SECRET

Possible drawbacks

None

Applicable issues

• fixes [bitnami/harbor] Invalid logic prevents assignment or auto-generation of REGISTRY_HTTP_SECRET in harbor-registry secret #31008

Additional information

None

Checklist

• Chart version bumped in Chart.yaml according to semver. This is not necessary when the changes only affect README.md files.
• Variables are documented in the values.yaml and added to the README.md using readme-generator-for-helm
• Title of the pull request follows this pattern [bitnami/<name_of_the_chart>] Descriptive title
• All commits signed off and in agreement of Developer Certificate of Origin (DCO)

[github-actions]

This Pull Request has been automatically marked as "stale" because it has not had recent activity (for 15 days). It will be closed if no further activity occurs. Thank you for your contribution.

[github-actions]

Due to the lack of activity in the last 5 days since it was marked as "stale", we proceed to close this Pull Request. Do not hesitate to reopen it later if necessary.