Consider allowing host.docker.internal with the http protocol for local development

[r-marques]

Changes

• updates isValidWebhookUrl to allow using host.docker.internal with the http protocol
• updates the validator unit tests to check if http://host.docker.internal:3000 is a valid webhook url

This makes it possible to set webhooks for services running on the host when developing locally and running the engine with docker

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PR-Codex overview

This PR updates the validation logic for webhook URLs to include host.docker.internal as a valid hostname for HTTP requests, enhancing local development compatibility.

Detailed summary

• Added a test case in tests/unit/validator.test.ts to validate http://host.docker.internal:3000.
• Modified the validation logic in src/server/utils/validator.ts to include host.docker.internal in the list of allowed hostnames for HTTP.

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