insights: support only snapshots for compute type insight

Created by: coury-clark

Note: this is for a retrofit of our current API

The mechanics of the first version of the compute type insight are such that we want only the current (within a day) values, and only a single value. Since the current API returns timeseries, we will want to purge the old data each day so that the response can be naively inspected to construct categorical charts (bar, pie, etc). For this purpose, we will reuse the snapshot functionality.

When we create a compute type insight we will need to do the following:

1. Prevent any backfilling other than the current time (mark backfilled completed, and possibly queue up a snapshot)
2. Disable interval recording (set the next_interval value to something impossibly far in the future?)