Replace `or_ignore` in `simple_insert` with `simple_upsert` (#10442)

Now that we have `simple_upsert` that should be used in preference to
trying to insert and looking for an exception. The main benefit is that
we ERROR message don't get written to postgres logs.

We also have tidy up the return value on `simple_upsert`, rather than
having a tri-state of inserted/not-inserted/unknown.