evaluate update-related datastore functions for `check_complex_operations_allowed`

`opctx.check_complex_operations_allowed()?;` should be called in datastore methods that either do not paginate or paginate on behalf of the caller, particularly the [`artifacts_for_repo`](https://github.com/oxidecomputer/omicron/blob/4d5bdc6d348b27761348d763c4085f060bcefc18/nexus/db-queries/src/db/datastore/update.rs#L58) function. (Once #9106 lands we should be able to do this.)