Add option for non-GSP forecast

[jacobbieker]

Pull Request

Description

Takes from #101 the generalization of PVNet to forecast things other than GSP.

Fixes #

How Has This Been Tested?

Unit test

• [ ] 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[bot]]

Codecov Report

Attention: 4 lines in your changes are missing coverage. Please review.

Comparison is base (eaa94f7) 57.63% compared to head (9c6917e) 57.76%. Report is 2 commits behind head on main.

Files	Patch %	Lines
pvnet/models/multimodal/multimodal.py	66.66%	2 Missing :warning:
pvnet/models/base_model.py	75.00%	1 Missing :warning:
pvnet/utils.py	91.66%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #119 +/- ## ========================================== + Coverage 57.63% 57.76% +0.13% ========================================== Files 26 26 Lines 1702 1712 +10 ========================================== + Hits 981 989 +8 - Misses 721 723 +2 ```

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