Feed data to Frontend for Max User count activity
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## Summary
We need to pass the relevant data to the UI for Max User count activity. Depending on [this discussion](https://gitlab.com/gitlab-org/gitlab/-/issues/290202#note_619831095) or existing APIs we can opt for graphql or REST.
## Additional Context
1. https://gitlab.com/gitlab-org/gitlab/-/issues/290202
1. https://gitlab.com/gitlab-org/gitlab/-/issues/334689#note_619838538
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