fix(config): add doc/line context to parse errors

[Deeven-Seru]

Description

Add document index + line/column context to YAML config parsing errors so users can locate issues fast in multi‑doc configs. Errors now includedoc/line/col, resource name when available, and env‑var substitution points.

PR Checklist

• Make sure you reviewed CONTRIBUTING.md
• Make sure to open an issue as a bug/issue before writing your code
• Ensure the tests and linter pass
• Code coverage does not decrease (if any source code was changed)
• Appropriate docs were updated (if necessary)
• Make sure to add ! if this involve a breaking change

Fixes #2927

[gemini-code-assist]

Code Review

This pull request improves error reporting during configuration parsing by adding line and column details. Key changes include refactoring environment variable substitution and using YAML AST nodes for precise error locations in multi-document files. Reviewer feedback suggests optimizing the lineColumnAt function for better performance on large inputs and including the document index in YAML parsing error messages for improved consistency.