Restructures the "Highlighting" documentation (elastic#134439)

* Splits up and restructures the Highlighting page

* Fixes links

* Update docs/reference/elasticsearch/rest-apis/how-es-highlighters-work-internally.md

Co-authored-by: Liam Thompson <[email protected]>

* Update docs/reference/elasticsearch/rest-apis/how-es-highlighters-work-internally.md

Co-authored-by: Liam Thompson <[email protected]>

* Update docs/reference/elasticsearch/rest-apis/how-es-highlighters-work-internally.md

Co-authored-by: Liam Thompson <[email protected]>

* Update docs/reference/elasticsearch/rest-apis/how-es-highlighters-work-internally.md

Co-authored-by: Liam Thompson <[email protected]>

* Update docs/reference/elasticsearch/rest-apis/how-es-highlighters-work-internally.md

Co-authored-by: Liam Thompson <[email protected]>

* Applies suggestions from code review

* Fixes link

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Co-authored-by: Liam Thompson <[email protected]>

Author: kosabogi