Enable websocket_server system on Windows

[iche033]

The websocket server system, ported from gz-launch to gz-sim for Jetty (#2792), is disabled on Windows. It currently does not build due to a linking error.

When linked against websockets_shared, the Windows CI produces the error:

LINK : fatal error LNK1181: cannot open input file 'D:\bld\libwebsockets_1712216166246\_build_env\Library\lib\libssl.lib' [C:\J\workspace\gz_sim-pr-clowin\ws\build\gz-sim10\src\systems\websocket_server\gz-sim10-websocket-server-system.vcxproj]

Note that the websocket server plugin in gz-launch was never built on our Windows CI since libwebsockets is an optional dependency and our Windows CI does not have this library dependency installed.

Desired behavior

websocket_server system should build and run fine on Windows CI