What does this PR do?

Adds extend to toggleGroup

Where should the reviewer start?

styledToggleGroup

What testing has been done on this PR?

locally and wrote a test

How should this be manually tested?

locally

add

     extend: `
                border: 1px solid red;
                &:hover {
                  background-color: green;
                }
              `,

Do Jest tests follow these best practices?

• screen is used for querying.
• The correct query is used. (Refer to this list of queries)
• asFragment() is used for snapshot testing.

Any background context you want to provide?

There is a desire to be able to provide hover styling on the container of the toggle group

What are the relevant issues?

closes #7481

Screenshots (if appropriate)

Do the grommet docs need to be updated?

yes

Should this PR be mentioned in the release notes?

yes

Is this change backwards compatible or is it a breaking change?

backwards compatible