add back in pvnet ecmwf old model

[peterdudfield]

Pull Request

Description

• add back in old pvnet model
• add back in old pvnet ecmwf model
• add option to switch from models using ocf_data_sampler and ocf_datapipes
• added new test in

As there are code changes since 2.3.30 the old version, it would be great to run the models with no ocf_data_sampler on dev for a bit, just to check they are working similar to production

Helps withs #123

How Has This Been Tested?

CI tests

• 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

[Sukh-P]

LGTM!