chore {Performance}: Implement models for Blocks

[colinmurphy]

Overview

See #378

Long term goal is to improve performance of block rendering by creating WPGraphQL Models instead on a field level so blocks can be cached and re-used.

References

• See @justlevine experiment PR - feat!: implement block model  rtCamp/wp-graphql-content-blocks#31
• Prior art from wp-rest-blocks: https://github.com/spacedmonkey/wp-rest-blocks/blob/bafb87a86d723b5ec54440e6fd6feb7fd94d6879/src/data.php#L72
• For caching prior art from snapwp-helper: https://github.com/rtCamp/snapwp-helper/blob/48986fcab24a79cf0cc31514dfff951d2486bc57/src/Modules/GraphQL/SchemaFilters.php#L49-L52

[colinmurphy]

@justlevine

FYI set this task up so we can start scheduling these in the upcoming sprints.

Also see - https://github.com/wpengine/wp-graphql-content-blocks/issues?q=is%3Aissue%20state%3Aopen%20label%3A%22scope%3A%20performance%22

I have labelled anything performance related as "scope:performance"