[20291] Gather-send implementation Docs

[cferreiragonz]

Description

This PR updates the API of the Chaining Transports.

• Merge after: https://github.com/eProsima/Fast-DDS/pull/4537

Contributor Checklist

• [X] Commit messages follow the project guidelines.
• [X] Code snippets related to the added documentation have been provided.
• [X] Documentation tests pass locally.
• N/A Applicable backports have been included in the description.

Reviewer Checklist

• [ ] The PR has a milestone assigned.
• [ ] The title and description correctly express the PR's purpose.
• [ ] Check contributor checklist is correct.
• [ ] CI passes without warnings or errors.