Allow catalogs in any schema yml file

[ankit-khare-2015]

Resolves #11707

Problem

Catalog definitions are currently loaded only from a dedicated root-level catalogs.yml file.
This prevents users from defining catalogs in regular schema YAML files (for example, models/schema.yml), unlike groups, which can be defined in any schema YAML file.

Solution

This PR updates catalog loading so catalogs can be defined in any schema YAML file under project source paths, while preserving support for root catalogs.yml.

Changes included:

• Updated catalog loading logic in core/dbt/config/catalogs.py:
  • Continue reading root catalogs.yml if present
  • Also scan schema YAML files under project source paths (all_source_paths)
  • Merge all discovered top-level catalogs: entries
• Updated CLI integration in core/dbt/cli/requires.py:
  • Pass ctx_project.all_source_paths into load_catalogs(...) so runtime commands load catalogs from schema YAML files
• Updated schema validation in core/dbt/jsonschemas/resources/latest.json:
  • Added catalogs as a valid top-level key for resource YAML schema validation
• Added tests:
  • tests/unit/config/test_catalogs.py (new): verifies loading from schema YAML and merge behavior with root catalogs.yml
  • tests/functional/catalogs/test_catalogs_parsing.py: adds end-to-end regression proving catalogs from models/schema.yml are loaded and applied

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.

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