Show license badge for Gitlab.com member overview

Part of #6995 (closed)

Logic implemented according to Jeremy's comment:

The natural next question is to find which specific users are taking up seats and who those 8 users are. So, if I'm a group Owner, I should be able to go to Members and see which users are taking up a seat.

For GitLab.com:

• If I'm an Owner in the namespace, I should be able to see the "Is Using License Seat" label.
• This label should only surface if that user is using a seat for that GitLab.com namespace.

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team