Pipelined Recovery - Consumer Related Code

This includes the consumer-specific code for the producer-consumer
architecture for WAL replay that separates WAL decoding from the
recovery process, enabling parallel processing between different steps
 of replay.

The startup process act as consumer and will initiate the pipeline before
starting the redo loop inside PerformWalRecovery() and will connect to
the shm mq to receive the decoded records directly. Subsequently,
it will apply those records and keep on fetching new decoded records in
the main redo loop.

Finally, it will receive a shutdown message from the producer
(based on the consistency checks, the producer will take care of whether
to stop decoding or not). The consumer will exit the loop and later will
ask to fully shutdown the pipeline workers in FinishWalRecovery().

Author: Imran Zaheer <imran.zhir@gmail.com>
Idea by: Ants Aasma <ants@cybertec.at>

Author: imranzaheer612