new: outcfg: Sort all fingerprints

including the relays not found in the consensus. Also:

• rename generate fn to append_outcfg
• split the function so that it can be call from tests with an empty Relays vector
• add root_path as argument to the function to pass different root directories for tests
• replace some &str arguments by Path as reference, so that the functions can accept path in several formats

Closes #33 (closed)