Tenant Overview page documentation

What does this MR do and why?

The Switchboard team are releasing the first iteration of the Tenant Overview page (https://gitlab.com/groups/gitlab-com/gl-infra/gitlab-dedicated/-/epics/153). This documentation provides clarity on each field in the Tenant Overview Page and will grow alongside the page functionality

https://gitlab.com/gitlab-com/gl-infra/gitlab-dedicated/team/-/issues/6175

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