Add troubleshooting about windows mapped drives

What does this MR do?

I was working with a customer who was using a mapped drive in their build script, and had Runner using a non-administrator user account. Every time the job ran from GitLab, they'd get an error stating "The system cannot find the path specified." However if they logged on as the user, then ran the job from the command line it worked. It turns out this is an intended feature of running services on Windows, and you have to use the UNC path and not the mapped drive path. We had a couple other tickets where folks reported the same problem, so we should add this to the Windows runner troubleshooting section.

Related issues

None, but I do have the internal-only Zendesk ticket

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