Allow matching against sub-string of description field on auto job creation

[MrMickS]

This change adds a third option to selecting a template to use when performing auto job creation. A match is made against a sub-string of the repository description passed in the payload.

We needed this as it was found that, due to our naming conventions, the existing options didn't provide sufficient flexibility.

[javiplx]

Please add a help file under views/gitlab_web_hook_root_action. Fix the failing test is fairly trivial, but if you are not used to rspec and have any difficulties, I can do it for you.
Besides that, I would like to know some more details about your use case, that is, why none of the existing templates suits your needs. The target is to add an explanation to readme, so if you write it there, it is much better.
Besides that, I would like to know if you are actually using a patched version. The only place where project descriptions are used (autocreation/deletion for new branches) should not collide with your patch, but if you are currently using it we could be pretty sure about that on an empirical ground.

[jenkinsadmin]

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