Document and validate the Gitea admin password

[TannerGabriel]

Gitea now requires passwords to be longer than six characters (source). If this criterion is not met, the Gitea pod will crash repeatably (CrashBackOffLoop) with the following error.

[F] Failed to run app with [/usr/local/bin/gitea admin user change-password --username gitea --password gitea]: Password is not long enough. Needs to be at least 6

To avoid errors for our users, we should add the password criteria to the documentation and maybe even add validation in the values.schema.json file (check if the password is six characters or more).

Definition of done

• [ ] Password requirements are defined in the README
• [ ] Password length is checked in the values.schema.json file

[christian-kreuzberger-dtx]

This is a limitation of gitea, not the provisioner. I would therefore not enforce any validation within our helm chart. Just imagine someone with an older version of gitea that could all of a sudden no longer use that password, because our provisioner says "it's invalid".

Therefore I am against implementing a validation in our values.schema.json.

However, I think this should be documented as a Known Problem in README.md.