PLT-6408 Framework for job server (#6404)

* Added initial job server

* Added job server to be ran as part of platform

* Added test job to the enterprise repo

* Fixed job server not loading license

* Renamed job package to jobs

* Fixed TE not being buildable

* Added JobStatus table to database

* Changed fields used by JobStatus

* Added APIs to query job status

* Added config change listener to server

* Added option to run job server from Makefile

* Added ability to enable/disable jobs from config

* Commented out placeholder for search indexing job

* Fixed govet

* Removed debug messages and fixed job api init message

imports/placeholder.go

@@ -0,0 +1,6 @@
+// Copyright (c) 2017-present Mattermost, Inc. All Rights Reserved.
+// See License.txt for license information.
+
+package imports
+
+// This is a placeholder so this package can be imported in Team Edition when it will be otherwise empty