Hide the git panel by default from the stage group dashboards

Closes gitlab-com/gl-infra/scalability#1088

There aren't many stage groups who are interested in the git components. In fact, only 4 stage group dashboards have any data for this component. We should hide it by default.

• Snapshot of Continuous Integration group using default setting: https://dashboards.gitlab.net/dashboard/snapshot/7erJzvID4JqFOh7GD4P9VTBv06Cs10o9?orgId=1
• Snapshot of 4 groups having git data:
  • Editor: https://dashboards.gitlab.net/dashboard/snapshot/G0oA2uVDVpLGQM28X3FzbC76PVmNfS8C
  • Source code: https://dashboards.gitlab.net/dashboard/snapshot/NK0xTvSVrSC4e37ula8tUWkqtz1cYq4X
  • Access: https://dashboards.gitlab.net/dashboard/snapshot/Ug0YunMCMbnvvCQbZqdJ04S38Ak12ewK
  • Project management: https://dashboards.gitlab.net/dashboard/snapshot/qB5goF3AmuzUMD4Ne9S1AM0skoFM9Eyd