feat: add workflow to test readme generation (#6359)

# Description

Created a workflow to search for README.docify.md in the repo, and run
cargo build --features generate-readme in the dir of the file (assuming
it is related to a crate). If the git diff shows some output for the
README.md, then the file update wasn't pushed on the branch, and the
workflow fails.
Closes #6331

## Integration

Downstream projects that want to adopt this README checking workflow
should:

1. Copy the `.github/workflows/readme-check.yml` file to their
repository
2. Ensure any `README.docify.md` files in their project follow the
expected format
3. Implement the `generate-readme` feature flag in their Cargo.toml if
not already present

## Review Notes

This PR adds a GitHub Actions workflow that automatically verifies
README.md files are up-to-date with their corresponding README.docify.md
sources. Key implementation details:

- The workflow runs on both PRs and pushes to main
- It finds all `README.docify.md` files recursively in the repository
- For each file found:
- Builds the project with `--features generate-readme` in that directory
  - Checks if the README.md has any uncommitted changes
  - Fails if any README.md is out of sync

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Co-authored-by: Alexander Samusev <[email protected]>
Co-authored-by: Iulian Barbu <[email protected]>