* DataData DS: Add Frame type to Random Walk queries
* Time column should not be nullable
Conversion for the SQL (server-side) expression was failing with:
`failed to convert data frames to long format for sql: missing time field`
Because we weren't seeing a match at:
`if f.Type() == data.FieldTypeTime {`]
here:
acb0e6b609/pkg/expr/convert_to_full_long.go (L155)
The DataPlane docs (https://grafana.com/developers/dataplane/timeseries)
state that:
> - The Time field(s):
> - Should have no null values
So making the fix here
3bdcbc5d37