docs: fix poisition of some data classes pages in the docs

[MortGron]

Description

Some of the data classes pages had the wrong position in the table of contents.

Before:

After:

Checklist:

• Tests added/updated.
• Documentation updated. Documentation is generated from docstrings - these must be updated according to your change.
  If a new method has been added it should be referenced in cognite.rst in order to generate docs based on its docstring.
• The PR title follows the Conventional Commit spec.

[gemini-code-assist]

Code Review

This pull request updates several documentation files, including data_ingestion.rst, data_workflows.rst, functions.rst, postgres_gateway.rst, sequences.rst, and unit_catalog.rst, to standardize section header underlines from carets to dashes, and renames one section header in the data ingestion documentation. There are no review comments, and I have no feedback to provide.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.81%. Comparing base (bef4f27) to head (3646d9b).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2763      +/-   ##
==========================================
- Coverage   93.83%   93.81%   -0.03%     
==========================================
  Files         513      513              
  Lines       52620    52620              
==========================================
- Hits        49377    49363      -14     
- Misses       3243     3257      +14     

see 4 files with indirect coverage changes

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