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.

app/plugin_context.go

@@ -0,0 +1,17 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package app
+
+import "github.com/mattermost/mattermost-server/plugin"
+
+func (a *App) PluginContext() *plugin.Context {
+	context := &plugin.Context{
+		RequestId:      a.RequestId,
+		SessionId:      a.Session.Id,
+		IpAddress:      a.IpAddress,
+		AcceptLanguage: a.AcceptLanguage,
+		UserAgent:      a.UserAgent,
+	}
+	return context
+}