Add messages for config changes (#3803)

* Automatically label Wasmtime `Config` object changes

* Add the "Label Messager" github action

This allows us to have custom messages left in comments on issues and pull
requests when they get labeled with a specific label.

* Add a message for `wasmtime:config`-labeled pull requests

* CI: Consolidate issue/PR triage workflows

.github/label-messager.json

@@ -0,0 +1,3 @@
+{
+  "wasmtime:config": ".github/label-messager/wasmtime-config.md"
+}