feat: simplify health indicator usage

[weboko]

Description

Right now HealthIndicator is a bit chunky.

Users need to:

• to get value - waku.health.toValue() or waku.health.toString()
• to monitor changes - waku.health.addEventListener

Those things are cumbersome and are not aligned with Waku API vision.
#2067

Proposed Solution / Feature Design

• Expose just health value from waku as waku.health. That's it.
• Proxy health change events from waku.events.