Billing Page Add Annual Contract Amount

GIVEN I am a user with a Contract billing account
WHEN I look at the Billing page
THEN I can see my remaining Contract amount alongside my current charges

## Acceptance Criteria
- [ ] In the 'Account balance' section on the /Billing page, display additional fields for the 'Remaining Balance'
- [ ] Title 'Remaining Balance' with the (?) Icon
- [ ] On mouse-over on (?) display the overlay for annual contract information
- Overlay content: "Your annual contract for {{amount}} will be available until {{date}}.
Usage beyond this amount will be billed at the rates set forth in your Sales Order"
- [ ] Display remaining balance amount
- [ ] "You have {{remaining days}} Days left in your contract plan"

## Design
https://www.figma.com/file/i2P2Sm0QP8R7oAFhSFMpqI/Billing-Q2-2021?node-id=1756%3A0