feat: detect bun as runtime

[lukasholzer]

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Summary

Fixes Parts of https://github.com/netlify/buildbot/issues/2914

Adding bun here as a runtime to improve our heuristics and detection mechanism to see who is already using bun on our platform.

This is to add visibility that we can perform humio queries on the runtime field and see if someone is already using bun.

As you can already use it by manually installing it. (Bypassing the npm install with adding a NPM_FLAGS=--version and doing the install in the build command – this was the previous workaround to get pnpm support before we had it.)

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[4xposed]

I don't think this really addresses what's intended by https://github.com/netlify/buildbot/issues/2912 though