Adding regression test data for phenology

[davidorme]

This PR adds the regression test and development data for the phenology module to the pyrealm_build_data module. It provides three data files:

• pyrealm_build_data/phenology/FLX_DE-Gri_FLUXNET2015_phenology_inputs.csv: A 10 year time series of half hourly FluxNET inputs used to calculate potential GPP using the Subdaily P Model for the phenology calculations.
• pyrealm_build_data/phenology/DE_Gri_Grassland_example_subset.csv: A 10 year time series of daily data calculated from the half hourly inputs and then predictions of daily phenological variables.
• pyrealm_build_data/phenology/DE-GRI_site_data.json: Constant site data including coordinates, elevation and site constants for aridity and other phenological calculation constants.

These are a bit bulky (40 MB in total) but the demonstration implementation from @zhouboya uses a long period. We might want to cut it down later, but this is source package only data.

Fixes #354

Type of change

• New feature (non-breaking change which adds functionality)
• Optimization (back-end change that speeds up the code)
• Bug fix (non-breaking change which fixes an issue)

Key checklist

• Make sure you've run the pre-commit checks: $ pre-commit run -a
• All tests pass: $ poetry run pytest

Further checks

• Code is commented, particularly in hard-to-understand areas
• Tests added that prove fix is effective or that feature works

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 96.09%. Comparing base (1f315ba) to head (318dbf7).
Report is 500 commits behind head on develop.

Additional details and impacted files

@@             Coverage Diff             @@
##           develop     #360      +/-   ##
===========================================
+ Coverage    95.29%   96.09%   +0.80%     
===========================================
  Files           28       35       +7     
  Lines         1720     2766    +1046     
===========================================
+ Hits          1639     2658    +1019     
- Misses          81      108      +27     

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[j-emberton]

This looks fine and I'm happy to approve.