pre-rfc: Add log channels

[Xuanwo]

We used query_enabled to control whether we print query-related logs. But in RFC https://databend.rs/doc/contributing/rfcs/new-logging, we removed it. Instead, we unified all our logs to the same logger.

However, based on discussion with @everpcpc, their does have the need for different log channels:

• system log: how query/metasrv works internally
• user log: user's request/response, query content, etc for audit

Maybe we can introduce the concept of channels for users to config like crdb dos: https://www.cockroachlabs.com/docs/stable/logging-overview.html

Information I needed

• Channels that are needed inside the databend-query.
• Should the channel be non-overlapping? Do we need to have a channel that contains all logs?

[Xuanwo]

Cc @flaneur2020 @ZhiHanZ @everpcpc for more input.

[everpcpc]

I prefer the non-overlapping way.

[flaneur2020]

a non-overlapping way +1