Add type information to dbt's configs

[drewbanin]

Describe the feature

dbt should default to using a jinja native environment for parsing jinja-rendered fields out of .yml files. This includes:

• schema.yml files
• dbt_project.yml
• profiles.yml

Jinja's native environment will help coerce string values to their native types (int, float, boolean, etc). The most obvious immediate use-case is:

models:
  enabled: "{{ true if target.name == 'dev' else false }}"

We want this to return a boolean, not a string, and a jinja native env would help us do that.

This is a big big change, and i think it will make 95% of people really happy and 5% of people sad. We should verify that there's a sane upgrade path here, so if you have some currently working code like:

some_field: "{{ 'True' }}

you still have a recourse for rendering this as a string, rather than a boolean, once this change is live.

Describe alternatives you've considered

Make configs type-aware and coerce stringy input into an expected type.

Additional context

I have not yet completely wrapped my head around the exact nature of the jinja native environment behavior. Here are some things that I want to be true, that I would love to verify before we start working on this:

-- this should return a boolean True value
my-config: "{{ true }}"

-- this should return a string value [??]
my-config: "{{ 'True' }}"

-- this should return a string value
my-config: "{{ 'true' }}"

-- this should return an integer value
my-config: "{{ 123 }}"

-- this should return a string value [??]
my-config: "{{ '123' }}"

The lines marked [??] are places where I am presently unsure of the jinja native env behavior. We should think really really hard about the implications of this change.

As beneficial as I think this change will be, I don't know that we can ship it if there's no ability to return a stringy value like "True" or "123" in this context. As long as there's some sane way to do that, then I'm all for making getting a PR to address this issue merged.

Who will this benefit?

Dynamic models configurers

[drewbanin]

closed by #2312