Impression events via EventLogging
Adds impression events, expected to supersede recording impressions
via beacon/impression. Currently implemented alongside that feature.
Provides a new mixin to control impression event sample rates on a
Instead of loading EventLogging modules client-side, we construct a
URL that should be the same as the one sent by EventLogging
we send remains correct.
Must coordinate with the CentralNoticeImpression EventLogging schema.
Also moves EventLogging schema configuration to extension.json.