[bitnami/mlflow] add option to disable the mlflow auth db upgrade

[LennartPiro]

Description of the change

The initContainer "upgradeDBAuthInitContainer" is made optional

Benefits

The init step currently fails if the database has already been initialized.

Possible drawbacks

Applicable issues

• fixes #

Additional information

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)

[carrodher]

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