Provide SSH key per SAPSID instead of per Workloadzone

[enterprise-1701-d]

Customers want more security: so every SAP system should have its own SSH-key-pair not just the whole workload zone like today.

Describe the solution you'd like
The ssh-key per SAP-SID should be stored and obtained in a similar way like the SAP-Masterpassword during the SAP installation

Describe alternatives you've considered
adding the location of a SSH-public key file into the tfvars-parameter-file but that is manual key creation/copy of the file and parameterization --> manual steps are not desired