Get the cluster credentials

User Story:

As a deployer, I want to be able to:

• Get the credentials for the cluster that is going to be deployed

so that I can achieve

• Checking the installed cluster for installation completion
• Connect and administer the cluster that gets installed

Currently the Assisted Service generates the credentials by running the ignition generation step of the oepnshift-installer. This is why the credentials are only retrievable from the REST API towards the end of the installation.

In the BILLI usage, which takes down assisted service before the installation is complete there is no obvious point at which to alert the user that they should retrieve the credentials. This means that we either need to:

• Allow the user to pass the admin key that will then get signed by the generated CA and replace the key that is made by openshift-installer (would mean new functionality in AI)
• Allow the key to be retrieved by SSH with the fleeting command from the node0 (after it has generated). The command should be able to wait until it is possible
• Have the possibility to POST it somewhere

Acceptance Criteria:

• The admin key is generated and usable to check for installation completeness

• (optional) https://issues.redhat.com/link.to.spike
• Engineering detail 1
• Engineering detail 2

This requires/does not require a design proposal.
This requires/does not require a feature gate.