[20893] Prepare 3.0.x-devel to become master

[EduPonz]

Description

This PR prepares the 3.0.x-devel branch to become Fast DDS master.
Related PRs:

• [20893] Prepare 3.0.x-devel to become master Fast-DDS-docs#750
• [20893] Prepare 3.0.x-devel to become main Fast-DDS-python#122
• [20893] Prepare 3.0.x-devel to become master ShapesDemo#127
• [20893] Prepare 3.0.x-devel to become master Shapes-Demo-Docs#109

Contributor Checklist

• Commit messages follow the project guidelines.
• N/A: The code follows the style guidelines of this project.
• N/A: Tests that thoroughly check the new feature have been added/Regression tests checking the bug and its fix have been added; the added tests pass locally
• N/A: Any new/modified methods have been properly documented using Doxygen.
• N/A: Any new configuration API has an equivalent XML API (with the corresponding XSD extension)
• N/A: Changes are ABI compatible.
• N/A: Changes are API compatible.
• N/A: New feature has been added to the versions.md file (if applicable).
• New feature has been documented/Current behavior is correctly described in the documentation.
  • Related documentation PR: [20893] Prepare 3.0.x-devel to become master Fast-DDS-docs#750
• 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.
• Check CI results: changes do not issue any warning.
• Check CI results: failing tests are unrelated with the changes.

[elianalf]

I think the only missing thing to change is the fallback_branch in documentation-tests

[EduPonz]

CI will not pass in this PR so it does not make sense to run it.