Add Shared Storage trusted origins route to RoutesBuilder (#49126)

We add a route for /.well-known/shared-storage/trusted-origins to RoutesBuilder in order to test custom data origins for shared storage.

See the explainer update: WICG/shared-storage#198.

(This is a second attempt, after closing the failed #49112.)

tools/serve/serve.py

@@ -604,6 +604,7 @@ def add_mount_point(self, url_base, path):
             ("GET", "/.well-known/interest-group/permissions/", handlers.PythonScriptHandler),
             ("*", "/.well-known/interest-group/real-time-report", handlers.PythonScriptHandler),
             ("*", "/.well-known/private-aggregation/*", handlers.PythonScriptHandler),
+            ("GET", "/.well-known/shared-storage/trusted-origins", handlers.PythonScriptHandler),
             ("*", "/.well-known/web-identity", handlers.PythonScriptHandler),
             ("*", "*.py", handlers.PythonScriptHandler),
             ("GET", "*", handlers.FileHandler)