allow providing client_id when locking / providing the unique value from outside the library

[talarari]

right now the value of the redlock key is just a secure random id.
when not able to acquire a lock its useful to be able to know who is holding the lock, to troubleshoot bad locks
the way to do this is to append a client_id to the unique id , something like {client_id}_{uuid}

this way when failing to acquire a lock , we can read the key and see who holds the lock

a more general way to do this as a library would be to allow library users to provide a function to generate the unique id in options
this way i could build they key however i like and add the metadata i need

thoughts?

[leandromoreira]

Hi @talarari it seems to be reasonable, I guess extending the current library to accept a generator function would be nice.