[cbuild] Add command line option --frozen-packs

[jkrech]

Related to Open-CMSIS-Pack/devtools#1225 adding command line option --frozen-packs to csolution.

Invoking cbuild with the command line option --frozen-packs requires the program to invoke csolution convert with the command-line option --frozen-packs.

There is not additional functionality required to be added to cbuild.

expected outcome:
csolution shall fail if no *.cbuild-pack.yml file exists -> which in turn makes cbuild fail
csolution shall not write/update the *.cbuild-pack.yml file - and as a result may fail (project and cbuild-pack yml are not in sync) -> which in turn makes cbuild fail

This extension to the command line usage requires an update to the documentation.