feat(admin): add POST endpoint for suggested-chart-revisions
feat(admin): add POST endpoint for suggested-chart-revisions

Adds an endpoint so that clients can POST an array of chart configs, to
be added to the queue of pending chart revisions.

OurWorldInData/owid-grapher,OurWorldInData/owid-grapher,OurWorldInData/owid-grapher,owid/owid-grapher,owid/owid-grapher,OurWorldInData/owid-grapher,owid/owid-grapher,OurWorldInData/owid-grapher,owid/owid-grapher,owid/owid-grapher