Add scope to users endpoints

[Aergwyn]

Please add a scope to the api/v2/users/{user}/ endpoints to make them accessible.

[EVAST9919]

What case exactly do you mean?

[Aergwyn]

Using any of the user endpoints results in an invalid scope error.
As far as I know there are only two scopes at the moment (identify and friends.read) thus making those endpoints inaccessible.

[cl8n]

this should be almost identical to the identify implementation and pretty easy to do, if any new contributors want to try it

[nekodex]

To echo my comment from #4815:

Currently there's privileged information being returned by the API (e.g. account moderation info/metadata inside /users/xxx responses for users within the moderation group/etc) that we don't want third-party clients to get by default when granting basic "user read" permissions.

So we're gonna move out all the privileged info into separate permission group(s) first before we open up endpoints that could expose that data (so that for example, moderators don't accidentally leak privileged info to third-parties without realising).

[peppy]

Would be good to get some eyes on this before january if time is available.

[nanaya]

Added in #5700.