CAPY-889 Add xsmall to BpkPrice component

[toveadamsson]

Description
Currently, 16px is not available in Backpack Price. The minimun font-size available is 20px.
In this task, we should contribute to Backpack to include the 16px option, to be able to use it in our new Unified xSell components

• Added xsmall type and include new size in BpkPrice
• Updated unit test
• Updated snapshots
• Added stories

BpkPrice xsmall	styles

Remember to include the following changes:

• Ensure the PR title includes the name of the component you are changing so it's clear in the release notes for consumers of the changes in the version e.g [KOA-123][BpkButton] Updating the colour
• README.md (If you have created a new component)
• Component README.md
• Tests
• Accessibility tests
  • The following checks were performed:
    • Ability to navigate using a keyboard only
    • Zoom functionality (Deque University explanation):
      • The page SHOULD be functional AND readable when only the text is magnified to 200% of its initial size
      • Pages must reflow as zoom increases up to 400% so that content continues to be presented in only one column i.e. Content MUST NOT require scrolling in two directions (both vertically and horizontally)
    • Ability to navigate using a screen reader only
• Storybook examples created/updated
• For breaking changes or deprecating components/properties, migration guides added to the description of the PR. If the guide has large changes, consider creating a new Markdown page inside the component's docs folder and link it here

[github-actions]

Visit https://backpack.github.io/storybook-prs/3643 to see this build running in a browser.

[github-actions]

Browser support

If this is a visual change, make sure you've tested it in multiple browsers.

Generated by 🚫 dangerJS against 98817c4

[github-actions]

Visit https://backpack.github.io/storybook-prs/3643 to see this build running in a browser.

[github-actions]

Visit https://backpack.github.io/storybook-prs/3643 to see this build running in a browser.

[lucascomp]

LGTM!