[BUGFIX] Reset singletons in Extbase command

This patch fixes the handleRequest() method signature of
the Cli request handler by returning the response object
like it is expected by the RequestHandlerInterface.

When the request is returned the Bootstrap process will
reset the singletons which includes persisting of any
changed objects.

Resolves: #52092
Releases: 6.2
Change-Id: I78a507ab5b68ad67a85bf4a914494b39ea1407e1