Provide SSH key per SAPSID instead of per Workloadzone

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