Rename Button Pair to Button Group in order to align with USWDS

[caw310]

Description

The following work was identified from the audit of the converted form components.

Details

1. Change the name from Button-pair to Button group to better align with USWDS
2. Design
   • Add button pair to the MVP sketch library

Tasks

• Make the updates identified in the audit
• Review designs with PO and/or DSC
• Review designs with an accessibility specialist
• Address any comments from reviews, if necessary
• Comment on this ticket with content specifications (e.g. labels and error messages)

Acceptance Criteria

• Component design is complete and has been reviewed
• Accessibility considerations have been added to this ticket, if necessary
• Content specifications have been added to this ticket, if necessary
• Link to design has been added to this ticket and shared in Slack

[humancompanion-usds]

I've updated the title here to reflect the remaining work. The Button Pair component is in the Sketch library and is in sync.

[LWWright7]

Please add your planning poker estimate with Zenhub @danbrady