Adding EnsureBot plugin helper. (#10542)

* Adding EnsureBot plugin helper.

* Removing unessisary GetBot call.

* Moving to own file and error handling cleanup.

* Removing patch functionaliy. Plugins should manage their own bot account updates for now.

* Adding tests and cleaning up errors.

* Modify to not shadow err.

* Moving helpers to seperate interface.

* Feedback fixes

plugin/helpers.go

@@ -0,0 +1,17 @@
+// Copyright (c) 2015-present Mattermost, Inc. All Rights Reserved.
+// See LICENSE.txt for license information.
+
+package plugin
+
+import "github.com/mattermost/mattermost-server/model"
+
+type Helpers interface {
+	// EnsureBot ether returns an existing bot user or creates a bot user with
+	// the specifications of the passed bot.
+	// Returns the id of the bot created or existing.
+	EnsureBot(bot *model.Bot) (string, error)
+}
+
+type HelpersImpl struct {
+	API API
+}