Add current package selection syntax

[barton996]

resolves #6891

Problem

There are many use cases where it is useful to exclude models not in your package from your run selection.

There is no easy way to limit your selection to just models in your project without resorting to hardcoding in package names.

Solution

This change adds 'this' as a valid package selector, enabling statements like dbt ls -s package:this

Running the selector above will return just the models from the current project.

User documentation

User docs for this feature should be added here:
https://docs.getdbt.com/reference/node-selection/methods#the-package-method

The examples can be updated to look like this:

# These three selectors are equivalent
dbt run --select "package:snowplow"
dbt run --select "snowplow"
dbt run --select "snowplow.*"

dbt run --select "package:this"  # only run models in the current dbt project 

Checklist

• I have read the contributing guide and understand what's expected of me
• I have run this code in development and it appears to resolve the stated issue
• This PR includes tests, or tests are not required/relevant for this PR
• This PR has already received feedback and approval from Product or DX within #6891
• This PR includes type annotations for new and modified functions

[github-actions]

Thank you for your pull request! We could not find a changelog entry for this change. For details on how to document a change, see the contributing guide.

[barton996]

@dbeatty10 @graciegoheen @gwenwindflower

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.14%. Comparing base (bcbde3a) to head (502d661).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9270      +/-   ##
==========================================
- Coverage   88.22%   88.14%   -0.08%     
==========================================
  Files         181      181              
  Lines       22643    22645       +2     
==========================================
- Hits        19976    19961      -15     
- Misses       2667     2684      +17     

Flag	Coverage Δ
integration	85.43% <0.00%> (-0.15%)	⬇️
unit	62.31% <100.00%> (+<0.01%)	⬆️

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[jtcohen6]

@barton996 Thank you for this PR! :)

@aranke and I revisited the question of what syntax makes most sense here, and after some more discussion, we think we prefer package:this over package:. (despite what I said a year ago). If you're amenable to that change, let's make it happen.