rename {resource}_id guidance to `id`

[toumorokoshi]

inspired by: aip-dev/google.aip.dev#1063

For google, the convention of {resource}_id is well ingrained into the sdks, and changing that expectation would be harmful for customers and the generated clients.

For overall APIs, removing the need to unnescessary inclusions of the resource singular would reduce the cost of code generated tooling.

We should look at changing the guidance in the general AIPs. @rofrankel also has a doc that suggests that we may want to re-evaluate the naming scheme on a broader level (e.g. with the convention to have name).

[rofrankel]

+1, we have made this change at Roblox already (in addition to the name -> path one you referenced).

[trg100]

@rofrankel also has a doc

Interested to see this. Is it public somewhere?

[rofrankel]

Afraid it's not currently public; we've talked about making our AIPs public but no solid plan yet. Some of what we've been working on will be reflected in this repo though. :)

Also, regarding the original issue: there are other places this comes up, e.g. repeated Book books in a ListBooksResponse. Could books just be something like items?