Add missing e2e gem cache in e2e reporting jobs

What does this MR do and why?

Follow-up for Remove pipeline-common pipeline template inclus... (gitlab-org/quality/analytics/team#39 - closed). Currently, qa gem cache was only present for e2e test jobs but it is also required for reporting jobs.

Move cache definition to base .qa-install definition so it's automatically inherited if gem install for qa folder is performed.

References

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• gitlab-org/quality/analytics/team#39 (closed)

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