For Garbage Collection, cortx-rgw needs a MotrGC thread which
works concurrently to delete all the stale objects.
Added the MotrGC class and the interface to configure and start
GC workers.

Signed-off-by: Sumedh A. Kulkarni <sumedh.a.kulkarni@seagate.com>

For supporting concurrent IOs MotrGC need to have multiple GCWorker threads.
Introducing GCWorker class and changing the MotrGC interfaces to manage
all the worker threads.

Signed-off-by: Sumedh A. Kulkarni <sumedh.a.kulkarni@seagate.com>

Implemented the logic to spawn multiple GCWorker threads on startup,
and gracefully exit on shutdown.

Signed-off-by: Sumedh A. Kulkarni <sumedh.a.kulkarni@seagate.com>

We are bound to create MotrMetaCache objects as we are directly using
class methods during CRUD operations without checking if metadata caching
is enabled or not.
Earlier I was trying to not create meta cache objects which was breaking
the CRUD, so now reverting it to create those objects again.

NOTE: Ideally we should create MetaCache objects only if caching is enabled.

Signed-off-by: Sumedh A. Kulkarni <sumedh.a.kulkarni@seagate.com>

add code to fetch the max gc indices to create.
create and append the index name in gc index list.

Signed-off-by: Sumedh A. Kulkarni <sumedh.a.kulkarni@seagate.com>