[Peers] Tech Debt: Move Transport code to separate folder

[julianknutsen]

As a developer, I want the Transport code to be in a separate folder so that the folder structure matches the dependencies (making scope creep harder) and it is easier to separate it out if/when it is needed for other use cases (watchtowers?).

Definition of Done:

• transport/ subfolder containing all items transport related (encryption/handshakes/etc)

Tech Discussion:
Move Transport code and all its dependencies to a sub-folder.
This can live under peer/ for now, but cleaning up the file structure to match the dependencies can make it easier to maintain.