Allow to create ParticipantSid from String in user module

[trzeciak]

Hey, I want test/use this livekit-rust-sdk in c++ code.
To do this I create internal-rust-layer to expose some functionality, and extract it to c++.
I came across a problem to create ParticipantSid from String in user module,
therefore i purpose to add 'pub' in declaration of this type:

pub struct ParticipantSid(String);

pub struct ParticipantSid(pub String);

Do you think it is ok, or I should choose other way?

[theomonnom]

Answered in #251