[SaaS UserCap FE]: Add "Approve" button to pending members table
## Description In #333064 we listed the pending members awaiting approval in the Seat usage > Pending members tab. Now we want to add an "Approve" button to each pending member row. ### Pending members table | Issue | Concerns | | ------ | ------ | | #333064 | It only adds the table and list the users with badges | | #330027 (:point_left: you're here)| It adds the "Approve" button to each row in the table | ## Feature flag This feature will be implemented under the `saas_user_caps` FF. ## Designs :warning: _New Design_ :point_down_tone3: https://gitlab.com/gitlab-org/gitlab/-/issues/321934/designs/pending-alert.png#note_735382597
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