fix: extension-slot life cycle issue

[nielslyngsoe]

Extension-slots require an unknown set of properties to be set before it makes sense for them to start initialising extensions.
This life-cycle has been improved as of this PR. and fixes an issue on the user-workspace.

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (minor updates related to the tooling or maintenance of the repository, does not impact compiled assets)

Motivation and context

How to test?

Screenshots (if appropriate)

Checklist

• If my change requires a change to the documentation, I have updated the documentation in this pull request.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[leekelleher]

Tested out in all of the places where I'd noticed the issue yesterday, and the errors have gone. Backoffice is working as currently expected. 👍