docs: update endpoints to use file-routing approach (#5397)

- Move the original guides for creating endpoints and middlewares to sub-sections in the Endpoints category.
- Replace existing guides for endpoints and middlewares with the new approach.
- Update all endpoints-related snippets across docs to use this new approach.

www/apps/api-reference/components/Tags/Operation/DescriptionSection/index.tsx

@@ -72,7 +72,7 @@ const TagsOperationDescriptionSection = ({
         reportLink={formatReportLink(area, operation.summary)}
         className="!my-2"
         vertical={true}
-        question="Did this endpoint run successfully?"
+        question="Did this API Route run successfully?"
       />
       {operation.externalDocs && (
         <>

www/apps/api-reference/components/Tags/Paths/index.tsx

@@ -33,7 +33,7 @@ const TagPaths = ({ tag, className }: TagPathsProps) => {
   const { loading } = useLoading()
   // if paths are already loaded since through
   // the expanded field, they're loaded directly
-  // otherwise, they're loaded using the API endpoint
+  // otherwise, they're loaded using the API route
   let paths: PathsObject =
     baseSpecs?.expandedTags &&
     Object.hasOwn(baseSpecs.expandedTags, tagSlugName)