Updated maintainers, version and name to rocketpy

[giovaniceotto]

Pull request checklist

Please check if your PR fulfills the following requirements:

• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features)
• Build (python setup.py install) was run locally and any changes were pushed
• Lint (black rocketpy) has passed locally and any fixes were made for failures
• All tests (pytest --runslow) have passed locally

Pull request type

Please check the type of change your PR introduces:

• Bugfix
• Feature
• Code style update (formatting, renaming)
• Refactoring (no functional changes, no api changes)
• Build related changes
• Documentation content changes
• Other: Pre-release updates

What is the current behavior?

The file setup.py uses the name rocketpyalpha and does not contain maintainers.

What is the new behavior?

• Package name changed to rocketpy.
• Package maintainers added.
• Version on setup.py updated to 0.9.8.

Does this introduce a breaking change?

• Yes
• No

[giovaniceotto]

@Gui-FernandesBR, go ahead and merge this pull request when you feel its ready.