[Feature] Add a metric when a ReadClient resubscribe is triggered.

[bzbarsky-apple]

Feature description

In ReadClient::TriggerResubscribeIfScheduledwhen mIsResubscriptionScheduled is true and we trigger a re-subscribe, we whould log a metric for that.

Note that re-subscribes come with a string reason (e.g. "unsolicited message" for "we got a message from the server, so presumably it's around", but other reasons are also possible).

Platform

all

Platform Version(s)

No response

Anything else?

No response