Add a "required" option for the Labels tag

**Is your feature request related to a problem? Please describe.**
It is not possible to enforce that the \ tag is used at least once in an annotation.

**Describe the solution you'd like**
It would be great if there were a "required" option for \, like some of the other tags (eg \), so that I can enforce usage of \.

**Describe alternatives you've considered**
I can set "enable_empty_annotation" to true in the project config which does technically enforce use of the \ tag but this only works if \ is the only Control Tag in the annotation config, which is often not the case in real projects.

**Additional context**
There is currently a "maxUsages" option for \, perhaps a "minUsages" would be easy to add. It would also be more general-purpose than a "required" option because you could enforce a precise number of usages, eg 1, 2, 3, etc.