This patch changes INSERTs into compressed chunks to no longer
be immediately compressed but stored in the uncompressed chunk
instead and later merged with the compressed chunk by a separate
job.
This greatly simplifies the INSERT-codepath as we no longer have
to rewrite the target of INSERTs and on-the-fly compress leading
to a roughly 2x improvement on INSERT rate into compressed chunk.
Additionally this improves TRIGGER-support for INSERTs into
compressed chunks.
This is a necessary refactoring to allow UPSERT/UPDATE/DELETE on
compressed chunks in follow-patches.
4527f51e7c