MULE-7656 Allow Jetty connector implementation to be customized

Reintroduce unused import removed in 3.x that is still required in
3.5.x (these things wouldn’t happen if we worked on 3.5.x issues in
3.5.x branch)
Merge pull request #790 from mulesoft/MULE-7656

MULE-7656 Reintroduce unused import removed in 3.x that is still required in 3.5.x