Unify humble and jazzy branches into one (main)

[francocipollone]

Summary

In order to better maintain the repository for both ros distributions (and future ones) it is convenient to have only one branch.

Considerations

• andino_gz_classic package will be deprecated
• humble and jazzy branches will still be there for some time. Let's add a comment in the readme on each branch.

Tasks

• Unify branches into main - One branch to rule them all #298
• Make main branch the default one
• Add note in jazzy and humble branches
• Update downstream packages in the ecosystem (if any) to point to main instead
• New humble release
• New jazzy release