Reuse Large Buffers in MigrateSession

[vazois]

This PR tries to improve memory utilization and reduce fragmentation by reusing large buffers that were allocated across different migrate sessions.
The PR includes the following:

• Introduce NetworkBufferSettings which is used to define the network buffer size configuration (i.e. send and receive buffer) for both clients and server implementation.
• Augment the network stack to support user defined instances of LimitedFixedBufferPool (LBFP) and NetworkBufferSettings.
• Define and use a shared instance of LFBP for ReplicationManager and MIgrationManager.
• Introduce PURGEBP command to allow for user to purge the LBFP instances of ReplicationManager, MigrationManager and ServerListener.
• Add BPSTATS section in INFO to retrieve stats about the declared LBFP instances of ReplicationManager, MigrationManager and ServerListener at runtime.

Notes:

• There is an upper limit on the number of entries per level in the LimitedBufferPool which may cause fragmentation of the LOH due to the way we allocate and return buffers to the pool itself (shown below)

  garnet/libs/common/Memory/LimitedFixedBufferPool.cs

  Lines 55 to 61 in 68a7a85

  	if (Interlocked.Increment(ref pool[level].size) <= maxEntriesPerLevel)
  	{
  	Array.Clear(buffer.entry, 0, buffer.entry.Length);
  	pool[level].items.Enqueue(buffer);
  	}
  	else
  	Interlocked.Decrement(ref pool[level].size);

  The default limit is 16 entries which should be enough for common scenarios (i.e. up to 16 parallel migrate sessions and up to 16 replication sessions).

[badrishc]

See comments.