Add safeupdate extension

[notramo]

https://github.com/eradman/pg-safeupdate

[raddevon]

I think we would implement this in our compiler rather than by adding the extension. Here's an issue you can track: #3137

Here's a comment that would also give some context around how we're considering implementing this: #1773 (comment)

In short, instead of globally requiring a filter on insert and delete which would break composability, we are considering reporting it as a warning through a forthcoming linting system.