0.17.1: opt-in native env rendering

[jtcohen6]

Description & motivation

• Add reference docs for is_bool, is_number, is_native
• Update is_text and 0.17.0 migration guide with changelogs, callouts
• Reflects changes in make native env rendering opt-in dbt-core#2618

To do before merge

Confirm that the pseudo-code I wrote as examples actually works

Update: All the example code is working when I've checked out dbt-labs/dbt-core#2618. One catch: the freshness example for is_native works without the is_native filter. I'm guessing that the coercion-to-dict is already happening because of hologram. Can you think of a better example?

[clrcrl]

Can you also add these to dbt-jinja-functions (page).
In an ideal world they would not need to be updated in two places, but, alas!

[drewbanin]

Couple of comments here but all minor - looks good to me once those are addressed, but of course let me know if you disagree with any of them!

[jtcohen6]

@drewbanin Do you have any ideas for a better is_native example? A case where it's actually/uniquely needed

[drewbanin]

I can't think of a good use case where we'd want to recommend as_native over as_number or as_bool. Maybe the one use case is around returning tuple/list/dict/set values from a jinja expression? I think that's pretty uncommon....

[jtcohen6]

I spent too long trying to come up with a sane example where is_native is strictly necessary. In the end, I just removed its Usage section and added a note recommending as_bool or as_number instead.