Add Secureframe partnership override env var for transparency URL

[iansltx]

For #27309.

• Manual QA for all new/changed functionality
• Added automated tests

[codecov]

Codecov Report

Attention: Patch coverage is 88.23529% with 2 lines in your changes missing coverage. Please review.

Project coverage is 63.77%. Comparing base (f351cb2) to head (e7fe01b).
Report is 68 commits behind head on main.

Files with missing lines	Patch %	Lines
server/service/devices.go	81.81%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #27388      +/-   ##
==========================================
+ Coverage   60.05%   63.77%   +3.72%     
==========================================
  Files        1745     1745              
  Lines      165806   165827      +21     
  Branches     4535     4535              
==========================================
+ Hits        99568   105762    +6194     
+ Misses      58534    51813    -6721     
- Partials     7704     8252     +548     

Flag	Coverage Δ
backend	64.58% <88.23%> (+4.09%)	⬆️

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[lukeheath]

Since this story is still in drafting, it's up to @noahtalerman when we want to merge this.

[lukeheath]

@iansltx Converting this to draft since we're not 100% sure what the code needs to look like yet (still in drafting AFAIK).

[iansltx]

@lukeheath This passed through user story review last Tuesday, and spec'ing happened at/before USR so this got moved to estimated shortly thereafter. So this has been out of drafting for a bit already.

[lukeheath]

Okay I was just out of the loop and this is ready to merge.

[ksykulev]

Simple enough. Looks good to me 👍