fix 60 min hardcode NWP resolution in multimodal.py

[AUdaltsova]

Fix hardcoded time resolution for NWPs

Description

NWP time resolution was hard-coded to be 60 minutes. ocf_datapipes had been updated already, this is a matching update for PVNet.

• In pvnet/models/multimodal/multimodal.py:
  • Added nwp_interval_minutes as an optional argument
  • Added creation of nwp_interval_minutes if not passed for backward compatibility
  • Updated some type hints to reflect that NWP parameters are passed as DictConfigand not int
  • Some typos fixed in the comments
• In configs.example/model/multimodal.yaml:
  • Added nwp_interval_minutes
• In PVNet/README.md:
  • Updated dead links and fixed some typos
  • Re-written batch creation and training instructions to reflect updates in configs.example

Fixes #181

How Has This Been Tested?

• Trained with the updated multimodal.py

• Ran run.py with both updated and original configs to ensure both are working

• 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