Filter by groups and snapshots

[foolip]

After https://github.com/web-platform-dx/web-features/pull/1060 it would be good to have these filters:

• group:css to list all features that are directly or indirectly part of the CSS group. Since a feature can be part of multiple groups, the simplest way to implement this is probably to generate a list of groups per feature by walking the group parent chain. Then there's no need for the search feature to understand the hierarchy.
• snapshot:ecmascript-2015 to list all features in ECMAScript 2015. There's no hierarchy here.

This would address some use cases in https://github.com/GoogleChrome/webstatus.dev/issues/276.

cc @hvanops

[jcscottiii]

This data is now available with https://github.com/web-platform-dx/web-features/pull/1060

[jcscottiii]

Filtering by groups and snapshot works if the user types the query directly. The work to add it to the autocomplete will be in this separate issue

• https://webstatus.dev/?q=group%3Acss
• https://webstatus.dev/?q=snapshot%3Aecmascript-5