feat: release agent 0.5.1 and add favicon

agent/go/cmd/rmm-agent/main.go

@@ -23,7 +23,7 @@ import (
 	"time"
 )
 
-const agentVersion = "0.5.0"
+const agentVersion = "0.5.1"
 
 type config struct {
 	ServerURL        string

agent/go/cmd/rmm-agent/main_test.go

@@ -8,7 +8,7 @@ import (
 )
 
 func TestAgentVersionIsStable(t *testing.T) {
-	if agentVersion != "0.5.0" {
+	if agentVersion != "0.5.1" {
 		t.Fatalf("unexpected agent version %q", agentVersion)
 	}
 }