ElementalRegistration should have a Ready condition

[anmazzotti]

This is needed as an enabler for the SeedImage implementation, but it's also quite annoying as it is.
The problem is that after the ElementalRegistration has been created, the controller needs a bit of time to generate a secret with a private key to generate a registration token, and to fetch the CA cert.

Both information (token and CA cert) are needed when creating the agent config, so if you do it too quickly the config will not carry these fields.

Therefore the ElementalRegistration needs to have a Ready condition status to be waited upon.