Enhancement(membership): update choices for membership levels

[JacobCoffee]

What

https://github.com/python/pythondotorg/blob/fc856dd119b42852a5a91effeffd9b6338d6b279/users/models.py#L84-L91 is outdated and needs to have its choices fixed following the bylaw change in https://github.com/psf/bylaws/pull/4

[dorian-adams]

@JacobCoffee Just to clarify, are there users in the database with a membership type that’s planned for removal? If so, would it be helpful for me to create a function to convert those users to “basic” or some other type?

[JacobCoffee]

There are definitely managing members that would need to be converted to contributing members per the bylaw changes.