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.

vendor/github.com/harmony-development/shibshib/buf.gen.yaml

@@ -0,0 +1,12 @@
+version: v1
+managed:
+  enabled: true
+  go_package_prefix:
+    default: github.com/harmony-development/shibshib/gen
+plugins:
+  - name: go
+    out: gen
+    opt: paths=source_relative
+  - name: go-hrpc
+    out: gen
+    opt: paths=source_relative