the current connection setup is single and shared connection, the strand on that...

the current connection setup is single and shared connection, the strand on that single connection may cause a serialization.
it should be noted that per s3-request there are several redis-operation that may run on co-routine.
the redis-connection pool implement the guarded acquire/release APIs.

adding configuration : rgw_redis_connection_pool_size.
re-factor of redis-exec* function.

shared pointer for Redis connection pool

adding branch predication optimization for redis-pool/single-shared-connection condition

adding a warning-report-method for the case there is a blocking state upon empty connection pool.

Signed-off-by: galsalomon66 <gal.salomon@gmail.com>