Use Did type in message crate

[GHkrishna]

Resolves #1165

Use did_parser_nom's Did type in message crates instead of string so as to parse & verify DIDs upon message deserialization

[Patrik-Stas]

Hi @GHkrishna thank you for contribution!

Sorry for delayed feedback, I've just enabled the CI run - as you can see the project doesn't compile now, you will need to sync up the rest of the codebase with these changes (won't be huge amount of work, but might be scattered across the board).

Additionally you need to make sure your commits are signed off - see the failing DCO check https://github.com/hyperledger/aries-vcx/pull/1171/checks?check_run_id=23276330183

[Patrik-Stas]

Closing due inactivity, feel free to reopen and continue later.