Split off from T296415

AC:

• When the infobox is expanded, an event is logged:

{
  "$schema": "analytics.mediawiki.ipinfo_interaction/1.0.0",
  event_action: "expand",
  event_context: "infobox",
  user_editBucket: "...",
  user_groups: [ "users", ... ]
}

• when it's collapsed an event is logged:

{
  "$schema": "analytics.mediawiki.ipinfo_interaction/1.0.0",
  event_action: "collapse",
  event_context: "infobox",
  user_editBucket: "...",
  user_groups: [ "users", ... ]
}

Notes

1. See the current.yaml files in the subdirectories in https://gerrit.wikimedia.org/r/plugins/gitiles/schemas/event/secondary/+/refs/heads/master/jsonschema/analytics/mediawiki for numerous examples of JSON Schema schemas that are used in production
2. wt:Event Platform/Instrumentation How To is a step-by-step guide to creating a creating a schema and validating an event with it
3. https://www.mediawiki.org/wiki/MediaWiki-Docker/Configuration_recipes/EventLogging is a step-by-step guide to setting up your local development environment