added workflow only build the docs on pull requests to see issues before merging

[s3inlc]

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[Copilot]

Pull Request Overview

This PR adds a new GitHub Actions workflow to build MkDocs documentation specifically for pull requests targeting the "dev" branch. The workflow enables documentation validation and issue detection before merging changes.

Key changes:

• Creates a new workflow that triggers on pull requests to the "dev" branch
• Sets up a comprehensive build environment including Python, PHP, Node.js, and various documentation tools
• Generates API documentation from OpenAPI specs and PHP code before building the final MkDocs site

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