Initial admin user bootstrapping via the operator

[vmuzikar]

• The operator will create an initial admin user.
• The KC_ADMIN and KC_ADMIN_PASSWORD env vars will be used for that.
• The credentials will be stored in a Secret.
  • If the Secret doesn't exist, the operator creates it and generates a random password.
  • If the Secret already exists (was created by the user), the operator will use the credentials from it.
• The Secret name needs to explicitly show that it is only initial bootstrap admin user, e.g. InitilAdminCreds.
• Any changes to the Secret won't be reflected in KC after first boot. The Secret can be deleted by user if needed.

[andreaTP]

KC_ADMIN and KC_ADMIN_PASSWORD

[vmuzikar]

Related discussion: #8549

Needs to be re-iterated after that discussion is solved.