message: docs: remove Lua experimental tag
  Script away!
diff: Lua
  ===
  -.. attention::
  -
  - The Lua scripting HTTP filter is **experimental**. Use in production at your own risk. It is
  - being released for initial feedback on the exposed API and for further development, testing,
  - and verification. This warning will be removed when we feel that the filter has received enough
  - testing and API stability to call it generally production ready.
  -
  .. attention::
  By default Envoy is built without exporting symbols that you may need when interacting with Lua
  