deprecate: remove management-ui as it has been moved to an independent repo

[reubenmiller]

Proposed changes

Removing the management-ui example as it has been relocated to tedge-management-ui to help with project maintance and tracking new feature requests/issues etc.

Types of changes

• [ ] Bugfix (non-breaking change which fixes an issue)
• [ ] New example (non-breaking change which adds functionality)
• [ ] Improvement (general improvements like code refactoring that doesn't explicitly fix a bug or add any new functionality)
• [x] Documentation Update (if none of the other choices apply)

Checklist

• [x] I have read the CONTRIBUTING doc
• [x] I have signed the CLA (in all commits with git commit -s)
• [ ] I have added necessary documentation (if appropriate)

Further comments