UML diagrams

[casperdcl]

Describe your changes

• Add requirements needed to generate UML diagrams.
• Add a script that identify circular package imports.
• Ignore the output directory in the Git repo.
• Extract the UML diagrams 1) for each package in CIL, and 2) for CIL as a whole.
• Update the file path and add a nice error message if the file does not exist.

Describe any testing you have performed

Please add any demo scripts to CIL-Demos/misc/

Link relevant issues

• #1679

Checklist when you are ready to request a review

• [ ] I have performed a self-review of my code
• [x] ~I have added docstrings in line with the guidance in the developer guide~
• [ ] I have implemented unit tests that cover any new or modified functionality
• [ ] CHANGELOG.md has been updated with any functionality change
• [x] Request review from all relevant developers
• [ ] Change pull request label to 'Waiting for review'

Contribution Notes

Please read and adhere to the developer guide and local patterns and conventions.

• [x] The content of this Pull Request (the Contribution) is intentionally submitted for inclusion in CIL (the Work) under the terms and conditions of the Apache-2.0 License.
• [x] I confirm that the contribution does not violate any intellectual property rights of third parties