Improve surfaces ontology

[thure]

This PR extends the content ontologies of both the Topbar and the Sidebar:

• The Topbar now supports a menu on its far prop
• The Sidebar now uses an Accordion (which is not its own component in Fluent Blocks yet) and expects a title.

[changeset-bot[bot]]

🦋 Changeset detected

Latest commit: 5b8eebc942af6ea2745d916a4b78aaa93c68b83b

The changes in this PR will be included in the next version bump.

This PR includes changesets to release 2 packages

| Name | Type | | ---------------------- | ----- | | @fluent-blocks/react | Minor | | @fluent-blocks/schemas | Minor |

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