List available streams on local port(eg. 8888), rather than giving a 404.

[briantho]

Describe the feature

When running mediamtx and using any browser to do hls, webrtc, whatnot I've noticed something that should probably be changed. Currently when running http://serveraddress:8888 you get a 404. You have to put the stream name in to get anything. for example, if I put in http://serveraddress:8888/mystream where mystream is a stream i have, eyerything works as expected. If I put in http://serveraddress:8888 without a stream I get a 404. In my opinion, the 404 should say "thanks for using mediamtx" and give a list of streams, so one can simply click a link, and easily load the selected stream.

This would be nice, as it could display all configured streams, all in one page. Then, a user could just click a link, and be brought straight to the correct stream url. Basically, instead of typing http://serveraddress:8888/stream1 or http://serveraddress:8888/stream2 you could just get a list of all available streams all on one page, then clicking stream1 you would be redirected to http://serveraddress/stream1