Add a dedicated OTLP converter

[SungJin1212]

Is your feature request related to a problem? Please describe.
The current OTLPHandler uses a Prometheus converter, which appears to cause significant memory allocation during the conversion to the Cortex format.
The Benchmark results are here: #6977

Describe the solution you'd like
Add a dedicated OTLP Converter which directly converts OLTP to Cortex Format. This would allow us to skip the intermediate conversion from Prometheus format to Cortex.