fix: transform Headers object to Record type

[hmacr]

Closes #759

This is a pre-requisite for triggerdotdev/api-reference#108

✅ Checklist

• I have followed every step in the contributing guide
• The PR title follows the convention.
• I ran and tested the code works

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Testing

Verified that the headers filter works on HTTP trigger.

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Changelog

Transform Headers object to Record type.

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Latest commit: 9ccbb00

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