Provide telemetry integrations for Phoenix and Phoenix LiveView

[davydog187]

Phoenix and Phoenix LiveView ship with telemetry events that could be use to capture page_view and other types of events.

It would be great if Posthog had a simple integration where auser could easily generate page_view events server side. In order to provide the distinct user ID and other information, the user would need to provide some MFA callback that allows them to specify this data.

Additionally, this system should offload events to some process, which could then send events to Posthog in batches, outside of the critical path (See #31 for additional conversation here)

[rafaeelaudibert]

@cschmatzler in case you're interested :). I can't assign it to you directly, only if you comment in here :)
Make sure you start from the v2.0.0-branch branch. If you don't get to it, I'll probably implement it :)

For some inspiration: https://github.com/cschmatzler/hedgehog

[rafaeelaudibert]

BTW, v2.0.0 is now merged and we should add this to the master branch now!