MM-22782: Write fuzz testing for websockets (#14203)

* MM-22782: Write fuzz testing for websockets

* Moved to fuzz function

* incorporate review comments

* Remove some more comments

cmd/mattermost/main_test.go

@@ -0,0 +1,16 @@
+// +build maincoverage
+
+package main
+
+import (
+	"testing"
+)
+
+// TestRunMain can be used to track code coverage in integration tests.
+// To run this:
+// go test -coverpkg="<>" -mod=vendor -ldflags '<>' -tags maincoverage -c ./cmd/mattermost/
+// ./mattermost.test -test.run="^TestRunMain$" -test.coverprofile=coverage.out
+// And then run your integration tests.
+func TestRunMain(t *testing.T) {
+	main()
+}