Add CI_JOB_TOKEN to git abuse rate limiting docs

What does this MR do and why?

CI_JOB_TOKEN carries the same permission as the user who triggers the pipeline, and thus counts against the limit of unique projects downloaded as stipulated within the Git abuse rate limit setting.

This MR updates the docs to state this.

Closes https://gitlab.com/gitlab-org/modelops/anti-abuse/team-tasks/-/issues/508

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