Prepare for zero downtime migrations
lo and behold, it's finally here: we're going to enforce zero downtime migrations. This MR updates various guides to reflect this, as well as adding code necessary to allow for zero downtime migrations.
TODO:
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Update the "What requires downtime" guide to state how to work around downtime -
Add code for ignoring columns -
Update customer/user facing documentation to outline when downtime is necessary or not -
Document renaming columns -
Document removing columns -
Document changing column types -
Document changing constraints -
Document data migrations that might normally require downtime -
Update list of downtime migration approvers