Add include create_modular_peer_connection_factory.h where it is used

This would allow to remove declaration of the
CreateModularPeerConnectionFactory from peer_connection_interface.h and
move its definition close to the declaration.

Bug: webrtc:42220069
Change-Id: I80c4faae8c327b620464d3ac024e35fef03a9902
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6722516
Reviewed-by: Vasilii Sukhanov <vasilii@chromium.org>
Commit-Queue: Harald Alvestrand <hta@chromium.org>
Auto-Submit: Danil Chapovalov <danilchap@chromium.org>
Reviewed-by: Mirko Bonadei <mbonadei@chromium.org>
Reviewed-by: Harald Alvestrand <hta@chromium.org>
Reviewed-by: Lambros Lambrou <lambroslambrou@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1486805}