Define interface for new plugin info (add to validator)

[nataliecarey]

What

With the upcoming changes to the plugin page we need to update the validator so that plugin developers (including ourselves) can start adding the additional info.

This formalises the interface ahead of bringing this content into the new plugin page.

Why

So we have a defined interface for people to use and so that people relying on the validator before releasing can continue doing that.

Who needs to work on this

• Developer

Who needs to review this

• Developer
• Designer

Done when

• The structure of the information has been approved by a designer and developer
• The validator has been implimented.