Add support for egressing OTLP logs and metrics

[wiktork]

• Rather than egressing to storage or to an http endpoint, send logs and metrics to an OTLP collector endpoint.
• Would not support direct backend egress (e.g. Azure Monitor)

Possible approaches

1. Create a new out of process egress provider that egresses to OTLP endpoint.

• Does not require any major changes to dotnet-monitor, other than restricting egress providers to specific artifact capabilities.
• Forces an unnecessary serialization/out of proc transfer/deserialization of the artifacts

2. Create an in-proc egress provider

• Built-in providers only, no need to serialize/deserialize artifacts
• Need to figure out configuration

Other concerns:

• The current OTLP Metrics exporter requires the creation of System.Diagnostics.Metrics. Since dotnet-monitor is a managed implementation, it likely creates these implicitly and may interfere with exporting user metrics.