WIP: tombstone spec v2

[sunnya97]

Moved from: #3103

• Targeted PR against correct branch (see CONTRIBUTING.md)

• Linked to github-issue with discussion and accepted design OR link to spec that describes this work.

• Wrote tests

• Updated relevant documentation (docs/)

• Added entries in PENDING.md with issue #

• 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 #3416 into develop will decrease coverage by 0.02%.
The diff coverage is n/a.

@@             Coverage Diff             @@
##           develop    #3416      +/-   ##
===========================================
- Coverage    59.35%   59.33%   -0.03%     
===========================================
  Files          131      131              
  Lines         9868     9868              
===========================================
- Hits          5857     5855       -2     
- Misses        3639     3641       +2     
  Partials       372      372