[DISCUSS] Move Slack discussions to ASF official slack?

[Misty Stanley-Jones]

When we first started using Slack, I don't think the ASF Slack instance
existed. Using our own Slack instance means that we have limited access to
message archives (unless we pay) and that people who work on multiple ASF
projects need to add the Kudu slack in addition to any other Slack
instances they may be on. I propose that we instead create one or more
Kudu-related channels on the official ASF slack (http://the-asf.slack.com/)
and migrate our discussions there. What does everyone think?