init command should run create-ssp if oscal-model is set to ssp

[gvauter]

Describe the solution you'd like
The init command should run the create-ssp logic when the --oscal-model is set to ssp. This will allow a single command to fully initialize the repo for ssp authorthing. Currently a user needs to run the init command and then run the create-ssp command separately. A CLI flag can be used to "skip" the create-ssp flow if desired.

Describe alternatives you've considered
The commands could be run separately.