otlp exporters: missing some environment variables from spec in SDK

[blumamir]

Is your feature request related to a problem? Please describe.

According to the spec for otlp exporter environment variables, the following variable should be supported by the otlp exporter:

OTEL_EXPORTER_OTLP_INSECURE, OTEL_EXPORTER_OTLP_SPAN_INSECURE, OTEL_EXPORTER_OTLP_METRIC_INSECURE
OTEL_EXPORTER_OTLP_CERTIFICATE, OTEL_EXPORTER_OTLP_TRACES_CERTIFICATE, OTEL_EXPORTER_OTLP_METRICS_CERTIFICATE
OTEL_EXPORTER_OTLP_COMPRESSION, OTEL_EXPORTER_OTLP_TRACES_COMPRESSION, OTEL_EXPORTER_OTLP_METRICS_COMPRESSION
OTEL_EXPORTER_OTLP_TIMEOUT, OTEL_EXPORTER_OTLP_TRACES_TIMEOUT, OTEL_EXPORTER_OTLP_METRICS_TIMEOUT

If I am not mistaken, these exporter options are not currently being read and applied.

Describe the solution you'd like

Add the appropriate options to the 3 otlp exporters

Describe alternatives you've considered

Additional context

Not sure if the optional INSECURE options are relevant in JS:

Implementations MAY choose to not implement the insecure option if it is not required or supported by the underlying gRPC client implementation.

[dyladan]

I'm pretty sure @grpc/grpc-js supports both secure and insecure modes.

[svetlanabrennan]

I'm interested in this issue. This relates to my retry logic issue.