[SPIKE]: Document brief technical proposal on scope and solution of automated migration/version tests

[danjm]

• document 3-4 cases of regressions that could have been prevented by automated migration e2e tests
• explain why they would not have been caught by existing tests
• describe, in written form, the tests that would have prevented the regression: the assertions needed, the flows to automate, the fixtures needed
• propose a general system or set of guidelines

Output should be roughly 1-2 google docs pages of content. Can be done within github comments

[gauthierpetetin]

Hi @danjm , is this still something we want to keep in "Ready-for-Dev"?