Clarify the features for generating default label sets

What does this MR do?

• Split out the information regarding the label set that GitLab can generate
• Add information for the labels view in the Admin panel

Are there points in the code the reviewer needs to double check?

• Please ensure that the newly added section relating to the Admin area seems relevant
• Please verify adherence to the documentation styleguide

Why was this MR needed?

Documentation regarding default label sets was missing

What are the relevant issue numbers?

Closes #1865 (closed)

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• CHANGELOG entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the style guides
• Branch has no merge conflicts with master (if you do - rebase it please)
• Squashed related commits together

@markglenfletcher awesome! The thing is I tried it locally and while I created a new label in the admin area, when I generated the preset labels in an existing project, the admin area label did not appear among them. Bug or am I missing something?

Edit: Ok my mistake, this is happening on new projects only (as the docs already mention, but I failed to read it correctly )

Milestone changed to %8.11

Status changed to merged

mentioned in commit 2aad2f05