cli: bump grpc log level from WARNING to ERROR

[tbg]

gRPC is too verbose. We can "fix" that by changing this line:

cockroach/pkg/cli/start.go

Line 447 in d591a49

grpcutil.SetSeverity(log.Severity_WARNING)

It's unclear whether we'd be losing anything, though. I tend to think not because the final connection errors are always bubbled up to the dialer. See for example

#34155 (comment)

Jira issue: CRDB-4666

[tbg]

Done in #99191