native: sync `metrics` feature option + default

[JoshuaMoelans]

Description

The develop docs now state that metrics should be opt-out, such that calling the metrics API immediately captures without needing to explicitly enable. Auto-collected metrics should probably still be gated behind some integration option, so this needs to be validated.

Alongside this, we want to sync the option to native (as seen in this comment)

Tackling as a follow-up of #2631

[linear-code]

UNITY-218