Support the OTEL_LOG_LEVEL environment variable

[MrAlias]

Add support for the OTEL_LOG_LEVEL environment variable as defined in the specification.

Blocked by https://github.com/open-telemetry/opentelemetry-go/issues/1068

Part of https://github.com/open-telemetry/opentelemetry-go/issues/1698

[MrAlias]

Also blocked by https://github.com/open-telemetry/opentelemetry-specification/issues/2039. The logging levels we implement need to be compatible with other langauges.

[mehulparmariitr]

Cuurently is there any way to change log level for Golang?

[MrAlias]

Cuurently is there any way to change log level for Golang?

Register a logr.Logger with the desired logging level.