Show subgroup count for group
Description
When you first go to group it is not clear at first if that group has sub-groups or not. Sometimes a group or subgroup has no projects (only nested subgroups) and it gets confusing when nothing is shown, as you are not sure if you are looking at an empty group or just a group with no projects (only subprojects).
Proposal
Have a number bubble next to both the Projects and SubGroups tabs on the Group screen. For example https://gitlab.com/gitlab-org should show a (2) next to sub groups and whatever number of projects next to it