Include model tags in parsers as well as a list parameter to filter them

[chrishronek]

Please take a look at the issue I've attached. This will be a doozie - tags are just one selector type, but they feel the most applicable to our parsers.

In a dbt project, tags can be set in 3 places (see more info here):

• a properties.yml file
• a .sql file in the models directory
• a dbt_project.yml file

(I've checked the ones that this PR would take care of) - the question is: Do we want to do it this way? This feels like the most natural, but we should talk about the following:

• the other selector types besides tags (these may or may not apply to how the parsers are parsing)
  • path:
  • config:
  • test_type:
  • test_name:
• whether this will be too strenuous on the DbtDag and DbtTaskGroup process to do this in-memory

[chrishronek]

@jlaneve took a stab at the tags piece of selectors - not sure if this is how we wanted to do it, and it'd probably be best to discuss. I figured some of this (or all of it) would get implemented one way or another.

[chrishronek]

Implemented in another PR