feat(instrumentation-undici): add custom metric labels

[lionskape]

Fixes #2597

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[linux-foundation-easycla[bot]]

• :white_check_mark:login: lionskape / (4b70e420f05aaa3c22a3448f0b147f810e132373)

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[pichlermarc]

As mentioned in the linked issue #2597, we unfortunately, we cannot accept this PR right now until https://github.com/open-telemetry/opentelemetry-js/issues/4096 is addressed.

Please feel free to re-open a new PR once that issue has been addressed. Thanks!