Deprecate imageUrl and buttonTitle from Mini App Metadata

[gabrielayuso]

We're introducing many new metadata fields to farcaster.json.

imageUrl will be deprecated in favor of ogImageUrl for simplicity.

buttonTitle will be deprecated since clients can obtain the button title from the homeUrl's fc:frame meta tag.

When displaying a rich embed for a Mini App solely using the data from farcaster.json we propose using the ogImageUrl as the image and Open or Open ${name} as the button title. If the URL has an fc:frame then use the image and title provided there.