Set `track_remaining` even when no MeshCircuitBreaker matched for the proxy

[lobkovilya]

Motivation

Currently, the track_remaining metric is set when a MeshCircuitBreaker is matched for the proxy. However, it should also be set even when there is no MeshCircuitBreaker matched for the proxy. This will ensure consistent tracking of remaining connections and improve observability.

Implementation

• Update the logic to set track_remaining regardless of whether a MeshCircuitBreaker is matched for the proxy.
• Add tests to verify the behavior when no MeshCircuitBreaker is present.

Related

Follow-up to #12206

[bartsmykla]

Triage: This seems probably to be related to PolicyZero, but we should probably just do this setting even before introducing this policy as thanks to this metric we would know how much capacity is left (we could also put it in the dashboards)