MM-10703 Adding blank request context to plugin hooks for future use. (#9043)

* Adding blank request context to plugin hooks for future use.

* Rename RequestContext to Context

* Adding context to ServeHTTP and ExecuteCommand

* Fixing import cycle in test.

plugin/hooks.go

@@ -48,11 +48,11 @@ type Hooks interface {
 	//
 	// The Mattermost-User-Id header will be present if (and only if) the request is by an
 	// authenticated user.
-	ServeHTTP(w http.ResponseWriter, r *http.Request)
+	ServeHTTP(c *Context, w http.ResponseWriter, r *http.Request)
 
 	// ExecuteCommand executes a command that has been previously registered via the RegisterCommand
 	// API.
-	ExecuteCommand(args *model.CommandArgs) (*model.CommandResponse, *model.AppError)
+	ExecuteCommand(c *Context, args *model.CommandArgs) (*model.CommandResponse, *model.AppError)
 
 	// MessageWillBePosted is invoked when a message is posted by a user before it is commited
 	// to the database. If you also want to act on edited posts, see MessageWillBeUpdated.
@@ -62,7 +62,7 @@ type Hooks interface {
 	//
 	// Note that this method will be called for posts created by plugins, including the plugin that
 	// created the post.
-	MessageWillBePosted(post *model.Post) (*model.Post, string)
+	MessageWillBePosted(c *Context, post *model.Post) (*model.Post, string)
 
 	// MessageWillBeUpdated is invoked when a message is updated by a user before it is commited
 	// to the database. If you also want to act on new posts, see MessageWillBePosted.
@@ -73,17 +73,17 @@ type Hooks interface {
 	//
 	// Note that this method will be called for posts updated by plugins, including the plugin that
 	// updated the post.
-	MessageWillBeUpdated(newPost, oldPost *model.Post) (*model.Post, string)
+	MessageWillBeUpdated(c *Context, newPost, oldPost *model.Post) (*model.Post, string)
 
 	// MessageHasBeenPosted is invoked after the message has been commited to the databse.
 	// If you need to modify or reject the post, see MessageWillBePosted
 	// Note that this method will be called for posts created by plugins, including the plugin that
 	// created the post.
-	MessageHasBeenPosted(post *model.Post)
+	MessageHasBeenPosted(c *Context, post *model.Post)
 
 	// MessageHasBeenUpdated is invoked after a message is updated and has been updated in the databse.
 	// If you need to modify or reject the post, see MessageWillBeUpdated
 	// Note that this method will be called for posts created by plugins, including the plugin that
 	// created the post.
-	MessageHasBeenUpdated(newPost, oldPost *model.Post)
+	MessageHasBeenUpdated(c *Context, newPost, oldPost *model.Post)
 }