What problem does this address?

With the block.json file now a part of the Gutenberg repository (#35998) we can take advantage of this file and use it to auto-generate block.json reference documentation.

What is your proposed solution?

The current block metadata documentation page could be updated to replace the "Block API" section with details generated out of the block.json schema file

The explanations and examples in the header and footer can be maintained and just the inner content replaced by using TOKENs to delimit the section that is auto-generated. See the other API generation docs for examples where we already do this.