Update span names for OpentelemetryPhoenix

[danschultzer]

Stacked on #431 which needs to get in first. Check the latest commit for the changes here.

I don't see any convention for how span names should be handled for websocket events other than maybe using the messaging namespace, but I think we want the structure to be more in line with how span names usually look: {operation} {resource}

So instead of MyAppWeb.ResourceLive.Show.mount it becomes live_view.mount /resources/:resource_id (for events it'll be live_view.handle_event /resources/:resource_id hello.

This is a breaking change.

Changes

• Span names changed from {live_view_module}.{handler_function} to live_view.{handler_function} {route}
• Span names changed from {live_view_module}.handle_event {event} to live_view.handle_event {route} {event}