* [DOCS] Update ESQL metadata fields page
**esql-metadata-fields.md:**
- restructured from bullet list to table format for metadata fields
- added `_index_mode` and `_source` fields to available metadata
- improved field descriptions (more detailed)
- added "usage and limitations" section
- reorganized examples into subsections with headers
- added `_score` sorting example
- added tip box linking to search documentation
* 🚙Drive by updates to search functions ref page
moved tutorial link into tip box at top
added cross-reference to search overview documentation
minor text flow improvements and punctuation fixes
* Fix id typo
* Apply suggestions from review
Co-authored-by: Bogdan Pintea <sig11@mailbox.org>
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