[datasource] add MySQL datasource

[BohuTANG]

Summary

Add MySQL external datasource.

[leiysky]

Does datafuse have mechanism like FDW(Foreign Data Wrapper)?

It's necessary to support registering external data sources in catalog, with their specific attributes(e.g. host, port, url).

[BohuTANG]

Does datafuse have mechanism like FDW(Foreign Data Wrapper)?

It's necessary to support registering external data sources in catalog, with their specific attributes(e.g. host, port, url).

We are planning to refcator the datasource module to support more datasources.
Such as MySQL, it will be like:

ENGINE = MySQL('host:port', 'database', 'table', 'user', 'password')

And the ENGINE uri is stored in metastore, when we use one table we first to check it's uri from the metastore and select the right datasource(here is mysql datasource) factory.
BTW, @dantengsky planning working on it.

[Xuanwo]

No action to take for now. Let's move to discussion.