[DOCS] Move script and stored fields content to search fields page (#60826)

Changes:

* Moves `Retrieve selected fields` to its own page and adds a title abbreviation.
* Adds existing script and stored fields content to `Retrieve selected fields`
* Adds a xref for `Retrieve selected fields` to `Search your data`
* Adds related redirects and updates existing xrefs

docs/reference/scripting/fields.asciidoc

@@ -19,7 +19,7 @@ API will have access to the `ctx` variable which exposes:
 [discrete]
 == Search and aggregation scripts
 
-With the exception of <<request-body-search-script-fields,script fields>> which are
+With the exception of <<script-fields,script fields>> which are
 executed once per search hit, scripts used in search and aggregations will be
 executed once for every document which might match a query or an aggregation.
 Depending on how many documents you have, this could mean millions or billions
@@ -157,7 +157,7 @@ values are optimised for accessing the value of a specific field in many
 documents.
 
 It makes sense to use `_source` when generating a
-<<request-body-search-script-fields,script field>> for the top ten hits from a
+<<script-fields,script field>> for the top ten hits from a
 search result but, for other search and aggregation use cases, always prefer
 using doc values.
 =========================================================

docs/reference/scripting/using.asciidoc

@@ -18,7 +18,7 @@ the same pattern:
 <3> Any named parameters that should be passed into the script.
 
 For example, the following script is used in a search request to return a
-<<request-body-search-script-fields, scripted field>>:
+<<script-fields, scripted field>>:
 
 [source,console]
 -------------------------------------