Fix FireFox not streaming VPX on SPS

[lukehb]

Firefox was unable to stream VPX streams after upgrading to Firefox 128.0.

The details are contained in this PR from the PSInfra: EpicGamesExt/PixelStreamingInfrastructure#204

Relevant components:

• Scalable Pixel Streaming Frontend library
• Examples
• Docs

Problem statement:

Two problems:

1. Firefox was unable to stream when using VPX codecs.
2. Two config messages were being sent.

Solution

Two solutions:

1. Update SPS library to use lib-pixelstreamingfrontend-ue5.5 version 0.1.4, which contains the fix for Firefox being unable to stream VPX.
2. Unregister all config message listeners and add our custom config message listener that we use for handling the BrowserSendOffer configuration we get from our custom signalling server.

Documentation

I have updated the SPS docs in this repo to refer to pixelstreamingfrontend-ue5.5 as opposed to ue5.4 version/

Test Plan and Compatibility

Tested on:

Chrome + H.264 + CW = It streams
Chrome + VP8 + CW = It streams
FF + H.264 + CW = It streams
FF + VP8 + CW = It streams