Paid Newsletter and plans: Improve status and prorata

[crisbusquets]

Context: https://github.com/Automattic/jpop-issues/issues/9282#issuecomment-2445527662

Ideas mentioned

• Add a history of deleted/old plans in the Tools » Monetize » Payment Settings option. Or add a label with Active or Archived (or something similar) so the status is clear.
• Improve the modal, mainly the wording:
• 
• Provide more information about prorata cases to the site owner. See this comment. As Fab mentions: "Maybe "prorated price from previous subscription" will be better than "discount". Also letting the content-creator know in the receipt next to "earnings" could be helpful."