Allow urlText in DirectoryUpload

[dlmiddlecote]

Allow urlText to be set on a DirectoryUpload.

Adresses #3983

Contributor Checklist:

• I have updated the unit tests
• I have created a file in the master/buildbot/newsfragment directory (and read the README.txt in that directory)
• I have updated the appropriate documentation

[codecov]

Codecov Report

Merging #3990 into master will increase coverage by 0.03%.
The diff coverage is 20%.

@@            Coverage Diff             @@
##           master    #3990      +/-   ##
==========================================
+ Coverage   88.55%   88.59%   +0.03%     
==========================================
  Files         326      326              
  Lines       34321    34485     +164     
==========================================
+ Hits        30392    30551     +159     
- Misses       3929     3934       +5

Impacted Files	Coverage Δ
master/buildbot/steps/transfer.py	93.9% <20%> (-0.05%)	⬇️
master/buildbot/steps/worker.py	97.89% <0%> (-0.19%)	⬇️
master/buildbot/master.py	86.19% <0%> (-0.05%)	⬇️
master/buildbot/reporters/mail.py	95.78% <0%> (+1.63%)	⬆️

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[dlmiddlecote]

Nudge @tardyp