[soft-delete-namespaces] mark id_attr in metadata

[stopachka]

We want a way to restore namespaces.

Problem

Imagine if a user deletes two namespaces with the same name:

1. create posts { title }
2. delete it
3. create posts { title }
4. delete it

If we looked at the attrs, we wouldn't be able to disambiguate them between the "first" table and the "second" table.

Solution

To disambiguate, I added an id_attr_id at the time of an attr's deletion to the metadata.

Todos

• Add a sanity-check test for deleting the id attr
• won't do: Throw an error if we can't find the id attr

@dwwoelfel @nezaj @drew-harris

[dwwoelfel]

LGTM!

[stopachka]

Quick update: I added a sanity test deleting a full namespace. The other todo I had on the backend was to throw an error during deletes, if we don't find an id attr. I am thinking this may be a bit too harsh. I am a bit worried about throwing -- at least in tests we have lots of places where we don't use the id attr. My thinking is, the worst case scenario of the id attr not being found, is that the UI just won't show this deleted attr. It will be pretty easy to find it and restore it though.