Add timezones to forecast value creation datetimes

[lucasc896]

Pull Request

Description

This PR adds UTC timezones to the created_utc attributes of the returned forecast values, as discussed in this issue. No additional dependencies are required.

How Has This Been Tested?

Standard unit tests have been run.

• [x] Yes

Previous similar PR's haven't added any further logic to the unit tests, but would be happy to add some if required.

Checklist:

• [x] My code follows OCF's coding style guidelines
• [x] I have performed a self-review of my own code
• [x] I have made corresponding changes to the documentation
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] I have checked my code and corrected any misspellings

[peterdudfield]

@all-contributors please add @lucasc896 for code

[allcontributors[bot]]

@peterdudfield

I've put up a pull request to add @lucasc896! :tada: