Apply filter when scan SQL results

[dentiny]

Hi team, we've found OOM for metrics collector sidecar; reading through the code, it reads to me that

• Metrics collector for system metrics composes UNION SQL statements to clickhouse and get the data back
• Users are able to specify which system metrics to exclude, but these metrics are still pushed into in-memory Table, and only get filtered out right before written to prometheus writer

In this PR, to reduce the peak memory consumption, I move the filter logic before pushing into Table.