update expected power generation megewatts to 'real'

[peterdudfield]

Pull Request

Description

Update 'expected_power_generation_megawatts' in forecast_value to 'real' type. This make it less data to transfer.

TODO: add migrations scrips

Helps #116

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• [ ] Yes

If your changes affect data processing, have you plotted any changes? i.e. have you done a quick sanity check?

• [ ] Yes

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

[codecov-commenter]

Codecov Report

Merging #118 (487aa07) into main (81cade0) will increase coverage by 0.00%. The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #118   +/-   ##
=======================================
  Coverage   98.34%   98.35%           
=======================================
  Files          20       20           
  Lines        1026     1032    +6     
=======================================
+ Hits         1009     1015    +6     
  Misses         17       17           

Impacted Files	Coverage Δ
nowcasting_datamodel/__init__.py	100.00% <100.00%> (ø)
nowcasting_datamodel/models/forecast.py	100.00% <100.00%> (ø)
nowcasting_datamodel/read/read_gsp.py	100.00% <100.00%> (ø)
nowcasting_datamodel/update.py	98.71% <100.00%> (+0.06%)	:arrow_up:

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