Add icon for Education category

[danirabbit]

Problem

applications-education is an out-of-spec icon that is returned by Appstream: https://github.com/iainlane/appstream/blob/9f6168914f48897ebe6421a3b61dfe67467cd32c/src/as-category.c#L300

Proposal

Create and gresource a symbolic icon for applications-education so that we can use category icons in AppCenter

Prior Art (Optional)

No response