Add `EDUCATION` as a `classification` in the `METADATA.pb` files

There was some discussion today about the need to add `EDUCATION` as a `classification` in the `METADATA.pb` files.

This came up while discussing the Playwrite family, which is an important upcoming typeface in the Google Fonts catalog, but it seems like this might be a unique enough category to warrant it's own classification tag.

Specifically for Playwrite, this came up while discussing how to approach abbreviations in family name vs. what shows up on front end. The ideas presented were:

- Metadata approach with full name that does not match nameID 4. Rosa thinks that this will work for any family, including non-Noto. Metadata field is display_name:
- Add classification field for educational families to further support identification of these country/region-specific model families as intended for education purposes.

@vv-monsalve might have more context if needed