Update Project Members API rate limit to 200 requests/minute

What does this MR do and why?

We've encountered customer feedback due to the new rate limits for retrieving project members via the API. We initially chose 60 requests per user per minute, but this has caused migration challenges for some customers who need to call this endpoint more frequently than this.

We think 200 requests per minute is still a reasonable safety measure for GitLab while allowing customers the ability to query their data more frequently.

References

• Issue discussing the rate limit
• MR which introduced the change
• MR which updated docs

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