docs: add webhook documentation

[AkashKumar7902]

What has changed?

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This PR Resolves #(issue)

Type of change

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• Bug fix (non-breaking change which fixes an issue).
• New feature (non-breaking change which adds functionality).
• Breaking change (fix or feature that would cause existing functionality to not work as expected).
• Documentation update (if none of the other choices apply).

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Checklist:

• My code follows the style guidelines of this project.
• I have performed a self-review of my own code.

[keploy]

To generate Unit Tests for this PR, please click here.

[Copilot]

Pull Request Overview

This PR adds comprehensive webhook documentation for Keploy ATG (Automated Test Generation), specifically focusing on the webhook integration system. The documentation provides developers with the necessary information to implement custom webhook servers that can integrate with Keploy's test execution lifecycle.

• Introduces a complete webhook integration guide with concepts, API reference, and examples
• Provides a working Go server implementation demonstrating webhook handling patterns
• Documents the two-phase webhook system (PreExecute and PostExecute) with detailed data structures

[Copilot]

This paragraph appears to be unrelated content that was accidentally included in the documentation. It references implementation details about DTOs and internal models that don't match the context of the webhook documentation.

Suggested change

Of course. Since you are not using a separate DTO layer, the documentation must accurately reflect the internal `entModels` that will be serialized directly to JSON. This means exposing all fields as they exist in your Go structs.

[Copilot]

This sentence appears to be editorial commentary that should not be part of the final documentation. It reads like a note to the reviewer rather than content for end users.

Suggested change

Here is the completed "API Reference: Data Structures" section for your documentation, written to be precise and developer-friendly.

[Achanandhi-M]

Hey @AkashKumar7902 Any update about this PR?