Compatibility with flask async routes

[williamhakim10]

Currently, flask-admin does not easily support flask routes declared as async (see https://flask.palletsprojects.com/en/3.0.x/async-await/). While this isn't a dealbreaker, if you have a bunch of async code (e.g., if you're using flask-admin alongside a Quart app), then it's pretty annoying to have to manually wrap all your code in asyncio.run(...) (or loop.run_until_complete(...)). My understanding is that the limitation stems from the expose decorator which does not call ensure_sync. It would be nice if expose could wrap async functions, or if expose_async existed as an alternative. I'd be happy to help with a PR if either of these approaches seem reasonable.