async tsdb chunkswrite needs a configuration

[t00350320]

AFAK, vendor/prometheus has imported an async tsdb chunkswrite method. Related configuration is a hard code with "DefaultWriteQueueSize = 0". We'll add a configuration in yaml file.

[yeya24]

Yeah I think it makes sense to expose the configuration. @t00350320 Would you like to submit a PR?

[t00350320]

Yeah I think it makes sense to expose the configuration. @t00350320 Would you like to submit a PR?

yeah, i will do it.

[alanprot]

Closing this as the PR got merged.