[DOCS] Relocate scriptless runtime document (#68916)
[DOCS] Relocate scriptless runtime document (#68916)

* Reallocate runtime document

Reallocate document `runtime-fields-scriptless` from `runtime-search-request` to `runtime-mapping-fields`

* Move runtime without script section

Move runtime without script section to under the dynamic runtime mapping section

* Fix snippet formatting and remove discrete heading.

* Update test snippet.

Co-authored-by: Adam Locke <307aeda080a14583cb9612dfe6f91313cf00d7ca@elastic.co>
GlenRSmith/elasticsearch,GlenRSmith/elasticsearch,GlenRSmith/elasticsearch,GlenRSmith/elasticsearch,GlenRSmith/elasticsearch,robin13/elasticsearch,robin13/elasticsearch,robin13/elasticsearch,robin13/elasticsearch,robin13/elasticsearch