Resolve some Vue warnings related to prop type mismatches

What does this MR do?

Resolves a couple of Vue warnings. isEditable and editable are defined as props with type Boolean in a few components, but could, in fact, be null. Converting them to Boolean resolves this warning. See Screenshots below for the warnings that have been resolved.

Screenshots

Vue warnings that have been fixed (suppressed in prod, so these only appear locally):

and

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content