* add migration

* add not null constraint

* remove not null constraint and default value

* add site schema change

* filter garbage props for prop_key suggestions

* filter garbage props returned by StatsController.conversions/2

* add crm action to set prop allowlist

* use nullable allowed_event_props field instead

* filter garbage props in db query instead

* implement suggestion dealing with string input

* refactor the allowlist condition in db query

* improve test