Ease of Setup improvements

[TomPughe]

Pull Request

Description

This issue includes some feature improvements to tackle issues I encountered when trying to run the module for the first time.

This is my first contribution to this code base so happy to get feedback on code style or any other aspect of my change

Features

• Adds details of required environment variables required for running unit tests
• Removes duplication of the folder name "latest" in utils by creating a function get_latest_subdir_path to retrieve the latest sub-folder name
• In the new function to retrieve the latest sub-folder name, allows optionally for the latest sub-folder to be created if it doesn't already exist. This is used in the existing function move_older_files_to_different_location which requires the folder to exist
• .gitignore update to cover files and folders created by the tool

How Has This Been Tested?

• A unit test has been added for get_latest_subdir_path and run locally
• Ran all unit tests locally to confirm they passed
• Re-Ran the instructions "Downloading EUMETSAT Data" to ensure the latest folder was created automatically

No Changes to data processing

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
• [x] 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 @TomPughe for code

[allcontributors[bot]]

@peterdudfield

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