Clarify that FLS/DLS disable shard request cache (#45462)

x-pack/docs/en/security/authorization/field-and-document-access-control.asciidoc

@@ -25,6 +25,9 @@ grant wider access than intended. Each user has a single set of field level and
 document level permissions per index. See <<multiple-roles-dls-fls>>.
 =====================================================================
 
+NOTE: Document- and field-level security disables the
+{ref}/shard-request-cache.html[shard request cache].
+
 [[multiple-roles-dls-fls]]
 ==== Multiple roles with document and field level security