Move group Labels menu item to Group information menu

What does this MR do?

In this MR, we are moving the menu item Labels from the Issues menu to the Group information one. These changes are behind a feature flag.

Refs #331008 (closed)

Screenshots (strongly suggested)

Before the MR:

After the MR:

Does this MR meet the acceptance criteria?

Conformity

• I have included a changelog entry, or it's not needed. (Does this MR need a changelog?)
• I have properly separated EE content from FOSS, or this MR is FOSS only. (Where should EE code go?)
• I have self-reviewed this MR per code review guidelines.
• This MR does not harm performance, or I have asked a reviewer to help assess the performance impact. (Merge request performance guidelines)
• I have followed the style guides.

Related to #21147 (closed)