[Gazebo] Display a new error in the repo page for FREE plans when all seats are taken

[RulaKhaled]

Problem: Users view a general error of "unauthorized error" if they can't view the page
Solution: All seats are taken screen

Conditions to render: User is not activated, viewing private repo, on free plans, no seats left.

Design: https://www.figma.com/file/veQ2bFZOFyvTao1OK3YfXN/Untitled?type=design&node-id=0-1&mode=design&t=KCRinLcN1Xzn0xGv-0

Tasks

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1. [API] Add a new hasSeatsLeft field to plan query #1318
   +0