Add liveSyncOnStallIncrease config option

[vk342]

This PR will...

add a new configuration option liveSyncOnStallIncrease to replace the constant currently used by LatencyController:

hls.js/src/controller/latency-controller.ts

Line 63 in 134b79b

const liveSyncOnStallIncrease = 1.0;

Why is this Pull Request needed?

Currently each time the player encounters a stall, targetLatency is incremented by 1 second, see

hls.js/src/controller/latency-controller.ts

Lines 63 to 69 in 134b79b

	const liveSyncOnStallIncrease = 1.0;
	return (
	targetLatency +
	Math.min(
	this.stallCount * liveSyncOnStallIncrease,
	maxLiveSyncOnStallIncrease,
	)

This PR replaces local const liveSyncOnStallIncrease = 1.0 with a value coming from hls.js config, as suggested here.

Are there any points in the code the reviewer needs to double check?

• validate that documentation for liveSyncOnStallIncrease makes sense.

Resolves issues:

Checklist

• changes have been done against master branch, and PR does not conflict
• new unit / functional tests have been added (whenever applicable)
• API or design changes are documented in API.md