Include plugin name in the log

[rickmak]

When we have multiple plugin in skygear system, the plugin logs are often mixed up. Make developer difficult to trace which plugin lead the the logged error.

• Skygear Server Date/Version: v0.24.0
• Application Platform: Skygear-server
• [ ] Is this a regression?
• [x] Attached logs, screenshots

Expected Results

Also print the plguin name the the log.

INFO[0000] Transport state changes from TransportStateUninitialized to TransportStateInitialized.  logger=plugin plugin_name=chat

Actual Results

INFO[0000] Transport state changes from TransportStateUninitialized to TransportStateInitialized.  logger=plugin
INFO[0002] Sending init event to plugin                  logger=plugin retry=1
INFO[0002] Transport state changes from TransportStateError to TransportStateUninitialized.  logger=plugin
INFO[0002] Get response from init                        err=Post http://127.0.0.1:9000: dial tcp 127.0.0.1:9000: getsockopt: connection refused logger=plugin out= plugin=&{initRetryCount:1 transport:0xc42025c380 gatewayMap:map[]}
INFO[0002] Transport state changes from TransportStateUninitialized to TransportStateError.  logger=plugin