feat: use keep alive connections

[wa0x6e]

🧿 Current issues / What's wrong ?

There's a lot of recurring connections to the same services, at a high rate.

• Sentry via SentryTunnel
• Snapshot-hub via the votes CSV generation

Opening a new connection on each request is costly, and create overhead, particularly on frequently requested url

💊 Fixes / Solution

We should reuse the connection when possible, by using a keep alive connection.

Fix #167
Fix #168
Fix SNAPSHOT-SIDEKICK-2
Fix SNAPSHOT-SIDEKICK-E

🚧 Changes

• Use node-fetch instead of cross-fetch (don't need browser support)
• Add a wrapper function to node-fetch, injecting keep-alive connection by using a custom agent.
• Use that custom fetch function whenever possible

🛠️ Tests

• Run yarn test:integration
• Not sure if HTTP interceptor can detect the keep-alive header correctly, but you can also try intercepting a request, such as curl -X POST localhost:3005/api/votes/0xa34107e34b4dc4ff4cd16b77d66e62a51f4d35457a4f4b1f68ab8ac821f58561

[codecov]

Codecov Report

Patch coverage: 72.00% and project coverage change: +0.39% 🎉

Comparison is base (417f011) 55.41% compared to head (17902d4) 55.80%.

❗ Current head 17902d4 differs from pull request most recent head 6727a5b. Consider uploading reports for the commit 6727a5b to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #166      +/-   ##
==========================================
+ Coverage   55.41%   55.80%   +0.39%     
==========================================
  Files          19       19              
  Lines        1570     1584      +14     
  Branches      111      114       +3     
==========================================
+ Hits          870      884      +14     
  Misses        691      691              
  Partials        9        9              

Files Changed	Coverage Δ
src/lib/metrics/digitalOcean.ts	0.00% <0.00%> (ø)
src/sentryTunnel.ts	0.00% <0.00%> (ø)
src/helpers/snapshot.ts	91.71% <100.00%> (ø)
src/helpers/utils.ts	57.62% <100.00%> (+13.18%)	⬆️
src/lib/nftClaimer/utils.ts	64.05% <100.00%> (ø)

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[Todmy]

utACK