Add rake task for updating fallback knapsack report for e2e specs

What does this MR do and why?

Add rake task to automate updates of master_report.json for knapsack fallback option.

While this report isn't used often, it is used as a fallback option in cases if appropriate report download from GCS failed or when adding new parallel jobs which don't have specific report yet.

Closes: gitlab-org/quality/quality-engineering/team-tasks#2506 (closed)

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