cryptography: Enable ability for a standalone build

[bramoosterhuis]

This is to break a cyclic build dependency between clientlibraries and libprovision, if we move to a vault implementation of libprovision. In existing builds, it will still build as part of clientlibraries. This just gives the option to invoke a build directly in Source/cryptography without moving cryptography in a separate repo.

Current cyclic dependency if we move to the vault powered libprovision:

• libproviosion -> clientlibraries(cryptography)
• clientlibraries(provisionproxy) -> libproviosion

[pwielders]

I think we can close this? @bramoosterhuis