Update project members page with tier info

Add tier and metadata info to project members page.

doc/user/project/members/index.md

 ---
-stage: none
-group: unassigned
+stage: Manage
+group: Access
 info: To determine the technical writer assigned to the Stage/Group associated with this page, see https://about.gitlab.com/handbook/engineering/ux/technical-writing/#assignments
 ---
 
-# Members of a project
+# Members of a project **(FREE)**
 
 Members are the users and groups who have access to your project.