bug: ydb_go_sdk_driver_conns metric does not clear old endpoints

[qrort]

Bug Report

YDB GO SDK version:

v3.101.0

Environment

linux, amd64

Current behavior:

when set of YDB dynnodes is changed, new endpoints are added to ydb_go_sdk_driver_conns metric, but the old ones, that are absent now, are not removed from it

Expected behavior:

ydb_go_sdk_driver_conns should list only endpoints, for which there is an alive connection in balancer connections pool

Steps to reproduce:

turn off one dynnode which is reported in ydb_go_sdk_driver_conns

Other information:

https://github.com/ydb-platform/ydb-go-sdk/blob/master/metrics/driver.go#L162

this code is not called, maybe because connections state is replaced on rediscovery here https://github.com/ydb-platform/ydb-go-sdk/blob/3074ad56386ccbcc0dc0b2f7cbe348bc01bb30f5/internal/balancer/balancer.go#L156 and Close() is not actually called