Add support for Harmony (#1656)

Harmony is a relatively new (1,5yo) chat protocol with a small community.
This introduces support for Harmony into Matterbridge, using the functionality
specifically designed for bridge bots. The implementation is a modest 200 lines
of code.

gateway/bridgemap/bharmony.go

@@ -0,0 +1,12 @@
+//go:build !noharmony
+// +build !noharmony
+
+package bridgemap
+
+import (
+	bharmony "github.com/42wim/matterbridge/bridge/harmony"
+)
+
+func init() {
+	FullMap["harmony"] = bharmony.New
+}