MM-12855 Plugin Context (#9922)

* Basic plugin context.

* Adding more useful fields to plugin context.

* Fix spelling

Co-Authored-By: crspeller <crspeller@gmail.com>

* Fixing location of context creation.

plugin/context.go

@@ -4,8 +4,12 @@
 package plugin
 
 // Context passes through metadata about the request or hook event.
-//
-// It is currently a placeholder while the implementation details are sorted out.
+// For requests this is built in app/plugin_requests.go
+// For hooks, app.PluginContext() is called.
 type Context struct {
-	SessionId string
+	SessionId      string
+	RequestId      string
+	IpAddress      string
+	AcceptLanguage string
+	UserAgent      string
 }