#7220049 Change labels in Memebership Subscription Page for one-time payment

Changes proposed in this Pull Request

Premium Content block has new type “One-time Payment”. In case using it showed to user messages are not relevant any more. This PR change label for this types to not confuse user.

Testing instructions

• Setup a wp.com simple or atomic site
• Go to wordpress.com/earn, connect to stripe etc,
• Add a premium content block
• Add a one-off payment plan called “Foo”
• Add another premium content block
• Add second monthly subscription plan called “Bar”
• Publish the post
• Open the site in a different browser, where you’re not logged in
• Press subscribe and fill out the form for “Foo”
• I get a message about making a one-off payment
• I can see the content
• Press subscribe and fill out the form for “Bar”
• I get a message about making a one-off payment
• I can see the content
• As the subscriber, I can see both payments “Foo” and “Bar” in https://wordpress.com/me/purchases/
• Go to details of “Foo” payment
• I can see “Product Details” instead “Subscription Details”
• I can see “Remove Foo product” instead “Stop Foobar subscription”
• I can click “Remove Foo product” and remove prodcut
• As the subscriber, I can see notification “This item has been removed.”
• Go back to https://wordpress.com/me/purchases/
• Go to details of “Bar” payment
• I can see “Subscription Details”
• I can see “Stop Bar subscription”
• I can click “Stop Bar subscription” and remove subscription
• As the subscriber, I can see notification “This item has been removed.”

Related to #62329