Migrate ros_gz_bridge documentation to gazebosim/docs per #708

[ShubhkarmanSingh7]

📝 Documentation Update

Resolves #708

Summary

Per the discussion and @j-rivero's suggestion in #708, I have removed the heavy documentation from the ros_gz_bridge README and replaced it with a clean pointer to the official gazebosim/docs site (https://gazebosim.org/docs/latest/ros2_overview/).

Note: I am opening a companion PR on the gazebosim/docs repository with the migrated Markdown content immediately after this.

Checklist

• Signed all commits for DCO
• Added a screen capture or video to the PR description that demonstrates the fix (as needed)
• Added tests
• Updated documentation (as needed)
• Updated migration guide (as needed)
• Consider updating Python bindings (if the library has them)
• codecheck passed
• All tests passed
• Updated Bazel files (if adding new files). Created an issue otherwise.
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