Making the QueryRequest Releasable

[alanprot]

What this PR does:
Follow up of #6808

• Extended QueryRequest message with buffer reference management capabilities
• Added defer req.Free() calls in QueryStream methods to properly release memory buffers
• Added new BenchmarkGrpcCalls benchmark function to measure gRPC call performance and memory allocations

Upon high query load, we can see a bunch of memory being allocated by those requests.

Looking at the code, we can see that is we turn on compression, the min size of the byte[] allocated to decompress is 32kb (which can add up quite fast).

https://github.com/grpc/grpc-go/blob/7472d578b15f718cbe8ca0f5f5a3713093c47b03/rpc_util.go#L878
https://github.com/grpc/grpc-go/blob/7472d578b15f718cbe8ca0f5f5a3713093c47b03/rpc_util.go#L922
https://github.com/grpc/grpc-go/blob/7472d578b15f718cbe8ca0f5f5a3713093c47b03/mem/buffer_slice.go#L262
https://github.com/grpc/grpc-go/blob/7472d578b15f718cbe8ca0f5f5a3713093c47b03/mem/buffer_slice.go#L28

The benchmark before and after shows exactly the 32K less bytes being allocated per request.

Before:

BenchmarkGrpcCalls-10    	    4092	    277700 ns/op	  105624 B/op	     520 allocs/op

After:

BenchmarkGrpcCalls-10    	    4204	    248313 ns/op	   72962 B/op	     516 allocs/op

Which issue(s) this PR fixes:
Fixes #

Checklist

• Tests updated
• [NA] Documentation added
• [NA] CHANGELOG.md updated - the order of entries should be [CHANGE], [FEATURE], [ENHANCEMENT], [BUGFIX]

[yeya24]

Thanks!