Add :read_jobs_statistics to GlobalPolicy

What does this MR do and why?

Describe in detail what your merge request does and why.

To avoid a huge MR at the end, I'm breaking up the work into several MRs to make reviews easier for everyone. The work is divided as follows:

step	MR
1	GraphQL: Add CI jobs statistics types (!107743 - merged)
2	GraphQL: Use specific connection type for runne... (!107744 - merged)
3	➡ Add :read_jobs_statistics to GlobalPolicy (!107747 - merged)
4	GraphQL: Expose jobs statistics in CiRunnersCon... (!107694 - merged)

Part of #377963 (closed)

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