[vtctldclient] Set SilenceErrors on the root command, so we don't double-log

[ajm188]

Description

What it says in the title. I noticed this while I was doing testing for #7395.

Before (SilenceErrors: false):

❯ vtctldclient --server "localhost:15999" DeleteKeyspace commerce >/dev/null
Error: DeleteKeyspace(commerce) error: rpc error: code = Unknown desc = keyspace commerce still has 1 shards; use Recursive=true or remove them manually; please check the topo
E0127 20:20:34.651188   89060 main.go:42] DeleteKeyspace(commerce) error: rpc error: code = Unknown desc = keyspace commerce still has 1 shards; use Recursive=true or remove them manually; please check the topo

After (SilenceErrors: true):

❯ vtctldclient --server "localhost:15999" DeleteKeyspace commerce >/dev/null
E0127 20:21:43.410431   89307 main.go:42] DeleteKeyspace(commerce) error: rpc error: code = Unknown desc = keyspace commerce still has 1 shards; use Recursive=true or remove them manually; please check the topo

Related Issue(s)

Checklist

• Should this PR be backported? No
• Tests were added or are not required N/A
• Documentation was added or is not required

Deployment Notes

Impacted Areas in Vitess

Components that this PR will affect:

• Query Serving
• VReplication
• Cluster Management
• Build/CI
• VTAdmin

[deepthi]

LGTM