Feature Request

Is your feature request related to a problem? Please describe:

When one downsteam IP is down , drainer can retry others IPs

Describe the feature you'd like:

Support to drainer syncer.to mysql host as multiple IP：

[syncer.to]
host = "127.0.0.1,192.168.0.1,192.168.0.100"

Describe alternatives you've considered:

Teachability, Documentation, Adoption, Migration Strategy: