Allow event subscribers to provide custom telemetry

In order for this module to be used by multiple Acquia projects, it's been requested that modules be allowed to send their own custom telemetry. We'll do that by using an event subscriber to provide our telemetry data, and allow modules to hook into that (provided they are listed in a hard-coded acceptlist of event subscriber classes, so as to prevent malicious or erroneous code from sending garbage to Amplitude).