Installing python modules correctly [20800]

[richiware]

Description

This PR improves the installation of the python module, especially on windows.

• Instead of install site-packages/fastdds.py, it install site-packages/fastdds/__init__.py. It's more python style.
• The user doesn't have to import the C++ DLL file himself (win32api.LoadLibrary()). It is the python module who did it now.

Contributor Checklist

• [x] Commit messages follow the project guidelines.
• [ ] 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
• [x] Changes are API compatible.
• [ ] 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.