Add Tugboat support [#3583330]

Problem/Motivation

As a user/contributor/site owner, it would be good to have MR environments to help with testing and evaluating solutions without needing to set up an environment locally.

Proposed resolution

Add the appropriate files to add support as outlined in the documentation at:
https://www.drupal.org/docs/develop/git/using-git-to-contribute-to-drupa...

Remaining tasks

Add the file
Add the Configuration to set up the tugboat environment

Issue fork seckit-3583330

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3583330-add-tugboat-support changes, plain diff MR !60
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