add horizon to csv route & format func

[braddf]

Pull Request

Description

Add forecast horizon params to CSV route to allow for latest and forecast_horizon as well as day_ahead.

N.B. This will change the default behaviour of the route to be latest, in line with other API routes unless specified in the query parameters, so we'll need to update the existing Day Ahead email before this is merged.

Fixes #

How Has This Been Tested?

• Test to follow next week.
• If your changes affect data processing, have you plotted any changes? i.e. have you done a quick sanity check?

Checklist:

• My code follows OCF's coding style guidelines
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have checked my code and corrected any misspellings

[peterdudfield]

raise 404 instead? or other appropriate error

[braddf]

It should raise a 400 at the top of this route handler if it's not one of the defined options – this was more to keep the inferred Python types happy because I don't think they can quite work out this should always hit one of these cases? 😅

[peterdudfield]

if we remove above - we should be using ForecastHorizon.horizon and this should raise a 400 then

[braddf]

Have stripped out the horizon option and doubled up on the 400 exception; feels like duplication, but can't see how else the inferred types could want this if we still want to validate at the start and return early if the param isn't valid (which we do)