feat: add category for createAPIClient and rename related markdown files

chore(docs): add `--create-api-client-fn` documentation for the context-based API client support

Author: radist2s

website/docs/codegen/openapi/create-api-client-function/_category_.json

@@ -0,0 +1,6 @@
+{
+  "label": "createAPIClient",
+  "position": 2,
+  "collapsible": false,
+  "collapsed": false
+}