cubicweb-collaboration #3814452 allow overloading of permissions in container, not just overriding [in-progress]

Currently permissions of entities/relations within container scope are just reset to the values defined in collaboration setup. It'd be useful if previously existing permissions could be kept, and collaboration ones added as mandatory RQL expressions.

prioritynormal
typeenhancement
done in1.0.0
load1.000
load left1.000
closed by<not specified>
patchReset groups in permissions when extended [applied]Handle overloading of RQLExpression for entity types and relation definitions [applied]Add mandatory rql expression for entity types within container [rejected]Add mandatory rql expression for container etype [rejected]Handle overloading of RQLExpression for entity types and relation definitions [folded]Issue a warning when existing permissions on etypes/rdefs are overridden by collaboration [rejected]Use CTN variable for container instead of C to avoid clashes in permissions extension [rejected]