tweak etcd selector for etcdHighNumberOfFailedGRPCRequests rule

Created by: junotx

What type of PR is this?

/kind bug

What this PR does / why we need it:

It workarounds frequent alerts with message etcd cluster "etcd": 100% of requests for Watch failed on etcd instance... for etcdHighNumberOfFailedGRPCRequests rule , which should be because etcd generates incorrect metrics (this pr https://github.com/etcd-io/etcd/pull/12196 has tried to fix it but it still exists after verification with the version after the pr)

/assign @benjaminhuo @pixiake