[Conesearch] Grouping of alerts require time column

[JulienPeloton]

When triggering a conesearch, the promise is that alerts will be grouped by ID, and only the latest one will be shown. But this is possible only if the time column is present. We should check this.

[jrob93]

Hi, this might be related - when I "Try it out" and "Execute" the /api/v1/conesearch example on https://api.lsst.fink-portal.org/ it fails with the following message:

{'status': 'error', 'text': 'You need to specify f:firstDiaSourceMjdTaiFink in the columns to filter on dates.\n'}

But when I do add the f:firstDiaSourceMjdTaiFink it runs and returns no matches.

As a side note, when looking up the issues I saw this and I agree that being able to conesearch on r:midpointMjdTai will be useful! I shall add a comment there too for the record.

[JulienPeloton]

Thanks @jrob93 for pointing out the faulty documentation! Actually, the coordinates in the test are old (commissioning data that does not exist anymore), and it should be replaced.

PR #173 will ship necessary modifications.