Resolve "Make dashboard secret generation generic"

Closes #143 (closed)

In stackspin:

• Install secrets controller.
• Create new kustomization per app for the secrets. Add a healthcheck for the secret that should be generated, so it waits for that secret to exist before marking the ks as ready.
• Make the app ks depend on that new ks. That way we know the secret exists before we attempt to install the app ks.
• Create secret templates (custom resources) for app secrets.
• Create secret templates (custom resources) for oauth clients/keys.
• Remove obsolete parts of install/generate_secrets.py.

In dashboard:

• Remove old secret generation.