Issue/86 move functions from ocf dashboard

[rachel-labri-tipton]

Pull Request

Description

Moves SQLAlchemy database functions from ocf-dashboard to the datamodel.

Fixes #86 (see also openclimatefix/analysis-dashboard#89

How Has This Been Tested?

pytests for the functions have passed

• 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

[peterdudfield]

so I think this fails at the moment due to linting, this can be fixing using the 'make format' and then checked with `make format'

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (51eb33b) 98.01% compared to head (037dabe) 98.33%.
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #87      +/-   ##
==========================================
+ Coverage   98.01%   98.33%   +0.31%     
==========================================
  Files          12       12              
  Lines         353      420      +67     
==========================================
+ Hits          346      413      +67     
  Misses          7        7              

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