Precip oi implementation

[richardarsenault]

Pull Request Checklist:

• This PR addresses an already opened issue (for bug fixes / features)
  • This PR fixes #xyz
• (If applicable) Documentation has been added / updated (for bug fixes / features).
  • If changes affect the GIS, Raven Modelling, Extremes.jl or Use Case Example notebooks, they have been re-run (ReadTheDocs will not update these).
  • If text has changed, make initialize-translations / make-translations.bat has been run and translations have been updated.
• (If applicable) Tests have been added.
• CHANGELOG.rst has been updated (with summary of main changes).
  • Link to issue (:issue:number) and pull request (:pull:number) has been added.

What kind of change does this PR introduce?

• This PR adds functions and tests for applying the optimal interpolation algorithm to a grid of precipitation by integrating information from station data.

Does this PR introduce a breaking change?

No

Other information: