CQs should execute one query with all intervals, rather than one query for each interval

[beckettsean]

Feature Request

Proposal: [Description of the feature]

CQs should run as efficiently as ad hoc queries.

Current behavior: [What currently happens]

Currently, a CQ like CREATE CQ RESAMPLE FOR 30m...GROUP BY time(5m) will create six individual queries, each covering a single 5 minute interval between now() and now() - 30m.

Desired behavior: [What you would like to happen]

A CQ like CREATE CQ RESAMPLE FOR 30m...GROUP BY time(5m) should create one individual query with a GROUP BY time(5m) clause and a WHERE time clause spanning the current 30 minutes.

Use case: [Why is this important (helps with prioritizing requests)]

Doing one query for each interval is a lot more queries, presumably worse for performance, and definitely not what the user expects to see. Even if the end result is the same, it's confusing and almost certainly less performant.