Add Alpha level Experimental Automatic Updates module

Please DO NOT push to this branch. See How to Help for instructions for working in the contrib module.

Problem/Motivation

Automatic Updates is one of Drupal Core current strategic initiatives

For full details of the initiative see #2940731: Automatic Updates Initiative overview and roadmap

Currently the work on the module is happening in 8.x-2.x branch of the Automatic Updates contrib module.

This issue is to bring in the current version of the 8.x-2.x branch of the contrib module into core as an Alpha level experimental module.

Proposed resolution

A merge request will be created on this issue that will mirror the 8.x-2.x branch of the contrib module. Because some things in the module will need to be altered to work in core the merge request commits will be created by a conversion script that will change things like the module machine name from automatic_updates to auto_updates

Since this is will be a very large merge request we will continue to create issues and make improvements in the contrib module 8.x-2.x branch and convert that work via the conversion script to commits here. @tedbow or @phenaproxima will make the conversion daily if there are commits to the contrib module.

How to help

Feel free to leave feedback on this merge request. If you would like to help address the feedback please search the 8.x-2.x issue queue to see if any existing issue exists and if not create one in that project.

Remaining tasks

1. Review the patch
2. Framework manager sign-off
3. Release manager sign-off

User interface changes

API changes

Data model changes

Release notes snippet