Consolidate `external` and `hideExternalIndicator` props into an `openInNewTab` prop or `target="_blank"`.

## Feature Description

See: https://github.com/google/site-kit-wp/pull/7847#discussion_r1402782242. More info to be filled out…

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## Acceptance criteria

* Base `Link` component:
* Accepts new prop `openInNewTab` prop to indicates that link should be opened in a new tab
* Accepts new prop `hasExternalIcon` to indicate that external icon should be included
* Existing `external ` and `hideExternalIndicator` props are removed
* Components using `Link` should be updated to use new props correctly

## Implementation Brief

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### Test Coverage

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## QA Brief

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## Changelog entry

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