Add initial Microsoft Teams support

Documentation on https://github.com/42wim/matterbridge/wiki/MS-Teams-setup

vendor/github.com/yaegashi/msgraph.go/beta/ExternalModel.go

@@ -0,0 +1,11 @@
+// Code generated by msgraph-generate.go DO NOT EDIT.
+
+package msgraph
+
+// External undocumented
+type External struct {
+	// Entity is the base model of External
+	Entity
+	// Connections undocumented
+	Connections []ExternalConnection `json:"connections,omitempty"`
+}