[REQ][php-lumen] Add Mock Server optional feature

Created by: ybelenko

Is your feature request related to a problem? Please describe.

I've successfully integrated Mock Server in php-slim4 and I'm going to add this feature to rest PHP server generators. If there are users or contributors who against it, please leave a comment.

Describe the solution you'd like

Add Mock Server feature(optional, disabled by default) to php-lumen server generator.

Additional context

Related issues #3545 (closed) and #6718 (closed)