Support OOB Proof Requests

[PaulWen]

OOB Proof Requests do not require a connection to be established beforehand.

[PaulWen]

According to etschelp it can likely be implemented by following this process:

Verifier:

1. /present-proof/create-request
2. /out-of-band/create-invitation (attachment id sollte dann die presentation exchange id sein, attachment type: present-proof)

Holder:

1. /out-of-band/receive-invitation