Add doc_blocks to manifest for nodes and columns

[aranke]

Resolves #11000
Resolves #11001

Problem

doc_blocks are not listed for node/column descriptions, so it's not possible to know if a description was created via literal or via doc block.

Solution

Add a new field doc_blocks for node and column descriptions that is present in the manifest.

doc_blocks is a list of unique IDs that can be accessed like so:

for uid in doc_blocks:
   doc_block = manifest.docs[uid]

I'll also update schemas.getdbt.com once this PR is approved to fix schema check errors below.

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 or 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.

[github-actions]

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[codecov]

Codecov Report

Attention: Patch coverage is 91.42857% with 3 lines in your changes missing coverage. Please review.

Project coverage is 88.87%. Comparing base (31881d2) to head (da9763f).

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #11224      +/-   ##
==========================================
- Coverage   88.92%   88.87%   -0.05%     
==========================================
  Files         187      187              
  Lines       24049    24072      +23     
==========================================
+ Hits        21386    21395       +9     
- Misses       2663     2677      +14     

Flag	Coverage Δ
integration	86.19% <91.42%> (-0.13%)	⬇️
unit	62.44% <17.14%> (-0.04%)	⬇️

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Components	Coverage Δ
Unit Tests	62.44% <17.14%> (-0.04%)	⬇️
Integration Tests	86.19% <91.42%> (-0.13%)	⬇️