Simplify rotation of passwords

[aledegano]

Is your feature request related to a problem? Please describe. As a Renku operator is quite labor intensive to rotate the passwords used by the various services to authenticate with each other as it is all manual. Namely the following passwords:

• Gitlab root password
• Keycloak admin password
• Postgres main password
• Gitlab database password
• Keycloak database password

Describe the solution you'd like As an operator I would like to only rotate the passwords in the values file and have an automated process change those secrets wherever necessary and -possibly- without any downtime necessary.

Additional context Kubernetes operators might be helpful to achieve what described above.

• https://postgres-operator.readthedocs.io/en/latest/
• https://www.keycloak.org/getting-started/getting-started-operator-kubernetes
• https://about.gitlab.com/blog/2021/11/16/gko-on-ocp/

Those operators might additionally remove the need of the "post-install" jobs.