Add primary_key to manifest

[dave-connors-3]

resolves #9824

Problem

This PR writes out the output of ModelNode.infer_primary_keys() to the manifest as a top level primary_key object.

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 no interface changes (e.g. macros, cli, logs, json artifacts, config files, adapter interface, etc) or this PR has already received feedback and approval from Product or DX
• This PR includes type annotations for new and modified functions

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 88.20%. Comparing base (84cc540) to head (446517a).
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #10096      +/-   ##
==========================================
- Coverage   88.23%   88.20%   -0.04%     
==========================================
  Files         181      181              
  Lines       22787    22805      +18     
==========================================
+ Hits        20107    20115       +8     
- Misses       2680     2690      +10     

Flag	Coverage Δ
integration	85.61% <100.00%> (+0.03%)	⬆️
unit	62.69% <73.68%> (+<0.01%)	⬆️

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[heysweet]

Talked offline with Dave, supportive of singular primary_key if that makes more sense in the data context!

[MichelleArk]

Artifact Schema Check should pass once dbt-labs/schemas.getdbt.com#39 is merged