Fix backwards description in runtime fields documentation (#94608) (#94642)

`runtime_mappings` is the name of the param in the search request. In the 
document `put` statement, it's called `runtime`

Co-authored-by: Matthew Hinea <matthew.hinea@gmail.com>

docs/reference/mapping/runtime.asciidoc

@@ -277,7 +277,7 @@ as part of the `runtime_mappings` section, just as you would if
 
 Defining a runtime field in a search request uses the same format as defining
 a runtime field in the index mapping. Just copy the field definition from
-the `runtime_mappings` in the index mapping to the `runtime` section of the search request.
+the `runtime` in the index mapping to the `runtime_mappings` section of the search request.
 
 The following search request adds a `day_of_week` field to the
 `runtime_mappings` section. The field values will be calculated dynamically,