Add SDK env variable for OTLP TLS skip verify

**What are you trying to achieve?**

I would like to configure OTLP exporter in SDK with env var to skip SSL verification. The variable is not currently supported https://opentelemetry.io/docs/specs/otel/protocol/exporter/ 

What did you expect to see?

**Additional context.**

Created from https://github.com/open-telemetry/opentelemetry-operator/issues/1818 


