Add start datetime parameter to gsp/pvlive endpoint

[devsjc]

Adds the start_datetime_utc parameter to gsp/pvlive to enable specification of a start datetime

[devsjc]

@braddf @rachel-labri-tipton Only thing I'm not sure about here is, if we're setting the usual number of days back that this endpoing can access behind an environment variable on the server side, perhaps there was the intention to keep whatever we set as N_HISTORY_DAYS as the maximum that a client-side user could ask for? This would overwrite that - so maybe I should put a block in to limit it? Or remove start datetime as an option and just change it to something like "snapshot" as a bool which just sets the startdate to last 15 minutes, preventing abuse?

@devsjc, I went ahead and ran the tests on this and the route looks good.
I could be missing something, but how is having a "snapshot" (which is better named that "historic") different from having the "historic" bool?

[devsjc]

@devsjc, I went ahead and ran the tests on this and the route looks good.
I could be missing something, but how is having a "snapshot" (which is better named that "historic") different from having the "historic" bool?

It might not be much better! It could just be better than target_datetime as an option as it would prevent a user trying to access the entire contents of the table with one call via a very early start_datetime_utc.

[peterdudfield]

@devsjc, I went ahead and ran the tests on this and the route looks good.
I could be missing something, but how is having a "snapshot" (which is better named that "historic") different from having the "historic" bool?

It might not be much better! It could just be better than target_datetime as an option as it would prevent a user trying to access the entire contents of the table with one call via a very early start_datetime_utc.

I like the idea of this, I would perhaps put the limit on, so that the user can get the whole history. Thats what PVlive is for. Could you do this @devsjc ?

[peterdudfield]

add limit, so can only pull at max 3 days of data

[peterdudfield]

This helps with #269