[media] Add option to specify port in http test server

This option allows tests to specify the port number when launching an
local http test server. This is useful to test requesting key systems
from different origins.

Change-Id: Ib7f997da003b94051639556478eaee6120db0e96
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/6219175
Reviewed-by: John Rummell <jrummell@chromium.org>
Commit-Queue: Feras Aldahlawi <feras@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1413828}