Add ability to change the label display when choosing the price

Problem/Motivation

Currently the label for the checkbox and text field is hard coded.

It's not always appropriately named and would be nice to be able to change via the UI.

Steps to reproduce

Proposed resolution

Add two additional settings that allow the labels to be changed via the UI.
Shift the current labels to defaultSettings
Add a settings summary so this displays in the admin screen.

Remaining tasks

User interface changes

Changes the manage form display page.
- Shows the selected options
- When editing the widget shows two additional fields.

API changes

Data model changes