Block Party

### Expected Behaviour
It would be nice to have a way for the community to submit blocks, code snippets etc.. that can help turbocharge development of Franklin sites for others. The criteria to get a block into the existing boilerplate / block collection is high and we still need a way to share and re-use blocks built by the community rather than re-inventing the wheel every project.

### Actual Behaviour
Currently need to search in github.com/hlxsites for similar blocks to then leverage in our own projects

Review the existing boilerplate and block collection, then compare them with community blocks in github.com/hlxsites. Define how contributors would submit, discover, and reuse blocks, and document the acceptance and maintenance process; completion requires a concrete, agreed scope for the proposed community collection.

Written by the indexing model from the issue text.