Rename `OTLPHandler` -> `OTelHandler`

[lzchen]

Our recommendations for users for logging would be to always use the OTLPHandler and then export using exporters that understand otlp logs.

Got some feedback that using OTLPHandler seemed confusing as it implies the only backend that logs can be sent to the collector, so a simple rename should clear this up. Open to different names too, as long as users know that this will be the "universal" handler that they should use to collect logs regardless of what exporter they are using.