[Cassandra] Orphan data check

[sylvlecl]

• Do you want to request a feature or report a bug?

Feature

• What is the current behavior?

It's easy to create data linked to a non existing node, for example:

    void testOrphanData() throws IOException {
        try (OutputStream outputStream = storage.writeBinaryData(UUIDs.timeBased().toString(), "DATA")) {
            outputStream.write("test".getBytes(StandardCharsets.UTF_8));
        }
    }

It can happen in real life situation if a client still has a reference to a deleted node.
Even if we add a check at write time, it could still happen because of concurrency issues.

• What is the expected behavior?

Provide an ORPHAN_DATA check in CassandraAppStorage. It will identify the data which are linked to a non existing node.
The repair will simply delete those data.

• What is the motivation / use case for changing the behavior?

Being able to identify and delete orphan data, which can waste some disk space.