[cryptography] Add test key generator

[sebaszm]

No description provided.

[pwielders]

I always like consistency :-) and my brain got an error by this construction :-D
Why do we always have ${NAMESPACE}Core::${NAMESPACE}Core and here only once (${NAMESPACE}Cryptography) without the semicolon. I understood from @bramoosterhuis that the first was the preferred way.
If so lets stick to that and always use for components that we as metrological deliver the ${NAMESPACE}Cryptography::${NAMESPACE}Cryptography to avoid my brain errors :-)

[sebaszm]

Fixed. Now need to educate myself on the difference. :)