Add zenity package

[mostlikelee]

#23585

Adding package for zenity command on Linux to be used in #23586 and will be manually tested in that task.

• Changes file added for user-visible changes in changes/, orbit/changes/ or ee/fleetd-chrome/changes.
  See Changes files for more information.
• Added/updated tests
• Manual QA for all new/changed functionality
• For Orbit and Fleet Desktop changes:
  • Orbit runs on macOS, Linux and Windows. Check if the orbit feature/bugfix should only apply to one platform (runtime.GOOS).
  • Manual QA must be performed in the three main OSs, macOS, Windows and Linux.
  • Auto-update manual QA, from released version of component to new version (see tools/tuf/test).

[codecov]

Codecov Report

Attention: Patch coverage is 37.19512% with 103 lines in your changes missing coverage. Please review.

Project coverage is 63.16%. Comparing base (8a8b840) to head (300b04d).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
orbit/pkg/execuser/execuser_linux.go	0.00%	69 Missing ⚠️
orbit/pkg/zenity/zenity.go	73.49%	22 Missing ⚠️
orbit/pkg/execuser/execuser.go	0.00%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #23619      +/-   ##
==========================================
- Coverage   63.20%   63.16%   -0.05%     
==========================================
  Files        1563     1564       +1     
  Lines      148874   149022     +148     
  Branches     3700     3700              
==========================================
+ Hits        94103    94135      +32     
- Misses      47351    47463     +112     
- Partials     7420     7424       +4     

Flag	Coverage Δ
backend	64.01% <37.19%> (-0.05%)	⬇️

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[lucasmrod]

First review pass done, left some comments!

The base branch was changed.