ADR: Add Source edit by reference endpoints

[samdbmg]

Details

Adds an ADR proposing how a Source-level edit-by-reference endpoint might behave, along with a partial implementation to illustrate one of the options.

Draft for discussion.

Pivotal Story (if relevant)

Story URL: https://www.pivotaltracker.com/story/show/188413555

Related PRs

N/A

Submitter PR Checks

(tick as appropriate)

• PR completes task/fixes bug
• API version has been incremented if necessary
• ADR status has been updated, and ADR implementation has been recorded
• Documentation updated (README, etc.)
• PR added to Pivotal story (if relevant)
• Follow-up stories added to Pivotal

Reviewer PR Checks

(tick as appropriate)

• PR completes task/fixes bug
• Design makes sense, and fits with our current code base
• Code is easy to follow
• PR size is sensible
• Commit history is sensible and tidy

Info on PRs

The checks above are guidelines. They don't all have to be ticked, but they should all have been considered.