Fix bug in handling traffic

[mostafa]

This is the log output of GatewayD when running it against the latest changes in this PR. It seems that the OnTrafficFromClient hook returns an error, which is swallowed until the server is killed or stopped.

Note
The SDK, Go template and the plugins should be tested with the new changes in this PR to ensure compatibility.

2023-10-16T13:22:20+02:00 WRN Running GatewayD in development mode (not recommended for production)
2023-10-16T13:22:20+02:00 INF configuring client automatic mTLS plugin=gatewayd-plugin-cache
2023-10-16T13:22:20+02:00 INF Starting metrics server via HTTP over Unix domain socket endpoint=/metrics plugin=gatewayd-plugin-cache timestamp=2023-10-16T13:22:20.157+0200 unixDomainSocket=/tmp/gatewayd-plugin-cache.sock
2023-10-16T13:22:20+02:00 ERR Failed to ping Redis server error="dial tcp 127.0.0.1:6379: connect: connection refused" plugin=gatewayd-plugin-cache timestamp=2023-10-16T13:22:20.227+0200
2023-10-16T13:22:20+02:00 INF configuring server automatic mTLS plugin=gatewayd-plugin-cache timestamp=2023-10-16T13:22:20.227+0200
2023-10-16T13:22:20+02:00 INF Registering plugin hooks name=gatewayd-plugin-cache
2023-10-16T13:22:20+02:00 INF Plugin is ready name=gatewayd-plugin-cache
2023-10-16T13:22:20+02:00 INF Started the metrics merger scheduler metricsMergerPeriod=5s startDelay=1697455345
2023-10-16T13:22:20+02:00 INF Starting plugin health check scheduler healthCheckPeriod=5s
2023-10-16T13:22:20+02:00 INF Metrics are exposed address=http://localhost:9090/metrics
2023-10-16T13:22:20+02:00 INF There are clients available in the pool count=10 name=default
2023-10-16T13:22:20+02:00 INF Started the client health check scheduler healthCheckPeriod=1m0s startDelay=2023-10-16T13:23:20+02:00
2023-10-16T13:22:20+02:00 INF GatewayD is listening address=0.0.0.0:15432
2023-10-16T13:22:20+02:00 INF Started the HTTP API address=localhost:18080
2023-10-16T13:22:20+02:00 INF Started the gRPC API address=localhost:19090 network=tcp
2023-10-16T13:22:20+02:00 INF GatewayD is running pid=1343

2023-10-16T13:22:25+02:00 ERR Database name not found or set in cache, startup message or plugin config. Skipping cache plugin=gatewayd-plugin-cache timestamp=2023-10-16T13:22:25.499+0200
2023-10-16T13:22:25+02:00 ERR Consider setting the database name in the plugin config or disabling the plugin if you don't need it plugin=gatewayd-plugin-cache timestamp=2023-10-16T13:22:25.499+0200
2023-10-16T13:22:25+02:00 ERR Database name not found or set in cache, startup message or plugin config. Skipping cache plugin=gatewayd-plugin-cache timestamp=2023-10-16T13:22:25.703+0200
2023-10-16T13:22:25+02:00 ERR Consider setting the database name in the plugin config or disabling the plugin if you don't need it plugin=gatewayd-plugin-cache timestamp=2023-10-16T13:22:25.703+0200
2023-10-16T13:22:28+02:00 ERR Database name not found or set in cache, startup message or plugin config. Skipping cache plugin=gatewayd-plugin-cache timestamp=2023-10-16T13:22:28.482+0200
2023-10-16T13:22:28+02:00 ERR Consider setting the database name in the plugin config or disabling the plugin if you don't need it plugin=gatewayd-plugin-cache timestamp=2023-10-16T13:22:28.482+0200
^C2023-10-16T13:22:30+02:00 INF Notifying the plugins that the server is shutting down
2023-10-16T13:22:30+02:00 INF GatewayD is shutting down
2023-10-16T13:22:30+02:00 INF Stopped health check scheduler
2023-10-16T13:22:30+02:00 INF Stopped metrics merger
2023-10-16T13:22:30+02:00 INF Stopped metrics server
2023-10-16T13:22:30+02:00 INF Stopping server name=default
2023-10-16T13:22:30+02:00 INF Stopped all servers
2023-10-16T13:22:30+02:00 ERR Cannot receive startup message error=EOF plugin=gatewayd-plugin-cache timestamp=2023-10-16T13:22:30.321+0200
2023-10-16T13:22:30+02:00 ERR Hook returned an error error="rpc error: code = Unavailable desc = error reading from server: EOF" hookName=HOOK_NAME_ON_TRAFFIC_FROM_CLIENT priority=1000
2023-10-16T13:22:30+02:00 ERR Database name not found or set in cache, startup message or plugin config. Skipping cache plugin=gatewayd-plugin-cache timestamp=2023-10-16T13:22:30.323+0200
2023-10-16T13:22:30+02:00 ERR Consider setting the database name in the plugin config or disabling the plugin if you don't need it plugin=gatewayd-plugin-cache timestamp=2023-10-16T13:22:30.323+0200
panic: runtime error: invalid memory address or nil pointer dereference
[signal SIGSEGV: segmentation violation code=0x1 addr=0x28 pc=0xb77762]

goroutine 129 [running]:
github.com/gatewayd-io/gatewayd/plugin.(*Registry).Run(0xc0002341c0, {0x17d00f8, 0xc0000fe0e0}, 0xc00049ff00?, 0x1?, {0x0, 0x0, 0x0})
        /gatewayd/gatewayd/plugin/plugin_registry.go:343 +0x8a2
github.com/gatewayd-io/gatewayd/network.(*Proxy).PassThroughToServer(0xc00058d110, {0x17d4be8?, 0xc0004aa008}, 0xc00025ab50?)
        /gatewayd/gatewayd/network/proxy.go:295 +0x366
github.com/gatewayd-io/gatewayd/network.(*Server).OnTraffic.func1(0xc0006c2d00, {0x17d4be8, 0xc0004aa008}, 0xc0004aa008?, 0x0?)
        /gatewayd/gatewayd/network/server.go:280 +0xa6
created by github.com/gatewayd-io/gatewayd/network.(*Server).OnTraffic in goroutine 51
        /gatewayd/gatewayd/network/server.go:277 +0x49b
exit status 2
make: *** [Makefile:98: run] Error 1