R4R: remove x/ dependency on cmd/gaia

[alessio]

This is an alternative patch to what is proposed in #4348

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.
• Wrote tests
• Updated relevant documentation (docs/)
• Added a relevant changelog entry: clog add [section] [stanza] [message]
• rereviewed Files changed in the github PR explorer

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For Admin Use:

• Added appropriate labels to PR (ex. wip, ready-for-review, docs)
• Reviewers Assigned
• Squashed all commits, uses message "Merge pull request #XYZ: [title]" (coding standards)

[codecov]

Codecov Report

Merging #4351 into master will decrease coverage by 0.02%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #4351      +/-   ##
==========================================
- Coverage   58.11%   58.09%   -0.03%     
==========================================
  Files         235      235              
  Lines       14882    14882              
==========================================
- Hits         8649     8645       -4     
- Misses       5605     5609       +4     
  Partials      628      628