add cache headers to /extended/v1/tx/:tx_id

[rafaelcr]

We currently don't add cache headers to /extended/v1/tx/:tx_id because its results may come from either the canonical chain or the mempool, and we don't have a cache handler that can deal with that variable scenario. This is causing that endpoint to produce spikes of ~10K uncached requests every ~10 minutes as some applications/marketplaces may be polling for some transactions continuously.

We should add an "adaptive" cache handler that would choose the correct ETag depending if the result came from the mempool or the canonical chain, and install it in that endpoint.

[blockstack-devops]

🎉 This issue has been resolved in version 4.1.0 🎉

The release is available on:

• npm package (@latest dist-tag)
• npm package (@latest dist-tag)
• GitHub release

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