Document hls.js and dash.js modules callbacks

[leroybm]

We have the following callbacks in the code, but only configureHls is documented.

                configureHls: (options) => {
                    return options;
                },
                onBeforeInitHls: (hls) => {
                },
                onAfterInitHls: (hls) => {
                },
                configureDash: (options) => {
                    return options;
                },
                onBeforeInitDash: (dash) => {
                },
                onAfterInitDash: (dash) => {
                }