Make the issuing of notification completely out of band with respect to
the `Pipeline`. Now the `StorageProvider` is responsible for providing
notifications to clients. Since some providers are local-only, there is
a `LOCAL_QUEUE` which allows sensing notifications through a local
queue, re-using the local revng daemon.
Instead of executing `chdir` when using the `-C` option, which is
fragile when other paths are involved, store the option in the click
context and propagate it to the required code paths that require knowing
what the base directory is.
Giacomo Vercesi