Add `into_tuple` to `SelectTwo` and `SelectTwoMany`

[miam-miam]

Motivation

Currently into_tuple only works on single Select queries. This leads to inconsistencies between the different query types and as such it should be extended to support the SelectTwo and SelectTwoMany queries.

Code like this should work

let res = Email::find_by_id(email_id)
        .select_only()
        .find_also_related(Thread)
        .column(thread::Column::Id)
        .into_tuple()
        .one(db)
        .await?;

Proposed Solutions

into_tuple should work the same as it currently does with Select

Current Workarounds

Currently you can query normally and get a struct in return but getting a tuple directly could help reduce code verbosity.

[ilxqx]

+1 I also need this method because after multiple join associations, I may only be concerned about a few fields.

[Expurple]

Maybe into_tuple() and similar methods should be moved into some trait to prevent such inconsistencies in the future?