tools/mmgotool: move into monorepo (#24010)

tools/mmgotool/go.mod

@@ -0,0 +1,10 @@
+module github.com/mattermost/mattermost/tools/mmgotool
+
+go 1.19
+
+require github.com/spf13/cobra v1.7.0
+
+require (
+	github.com/inconshreveable/mousetrap v1.1.0 // indirect
+	github.com/spf13/pflag v1.0.5 // indirect
+)