Add UM Global-NL path to NWP data sources

[katyalmohit]

Pull Request

Description

Add UM Global-NL to NWP data paths.

Fixes #407

How Has This Been Tested?

Tested locally with AWS

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]

Did you run the dashboard locally and check it worked?

[katyalmohit]

Did you run the dashboard locally and check it worked?

Earlier, I didn't update the lat_lon_datasets list, so that was throwing the error. Now, it's working.