Merge gaiareplay into gaiad to reduce number of binaries

[alessio]

• 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

---

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 #4272 into master will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #4272   +/-   ##
=======================================
  Coverage   59.09%   59.09%           
=======================================
  Files         217      217           
  Lines       14595    14595           
=======================================
  Hits         8625     8625           
  Misses       5332     5332           
  Partials      638      638

[sabau]

One more step on the path towards simplification 👍