Use python OTLP/proto metrics exporter once available

[aabmass]

Blocked by open-telemetry/opentelemetry-python#2447

Right now I have set the OTEL_METRICS_EXPORTER to none to fix #1148:

opentelemetry-operator/pkg/instrumentation/python.go

Lines 69 to 72 in 992b681

	// TODO: https://github.com/open-telemetry/opentelemetry-python/issues/2447 this should
	// also be set to `otlp_proto_http` once an exporter is implemented. For now, set
	// OTEL_METRICS_EXPORTER to none if not set by user to prevent using the default grpc
	// exporter which is not included in the image.

Once open-telemetry/opentelemetry-python#2447 is done, the operator's default should be updated to use the HTTP/proto exporter.

[vainikkaj]

Also by this open-telemetry/opentelemetry-python#3027
Both are merged but new release is needed.