refactor(go-website): implement redis caching of ecosystem counts

[michaelkedar]

Use the website redis to cache the ecosystem counts across Cloud Run instances.

• Store the ecosystem counts (and the time last fetched) in a new redis key that doesn't collide with the old Python ones.
• Added another key to track when the counts are being recomputed by any of the instances, to avoid every instance attempting to recompute the counts when it gets stale.
• Did NOT re-implement the rate-limiting through Redis. We're running on GCLB now, we should configure it at that level (if we even want it at all)

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[another-rex]

LGTM! No rate limits! _{just in gclb}