[carriers] add env carrier #2660

Job	Run time
opentelemetry-sdk	31s
opentelemetry-api	29s
opentelemetry-proto-gen-latest	17s
opentelemetry-opentracing-shim	20s
opentelemetry-getting-started	20s
opentelemetry-semantic-conventions	20s
opentelemetry-exporter-otlp-proto-common	19s
opentelemetry-exporter-zipkin-combined	20s
opentelemetry-exporter-zipkin-proto-http	20s
opentelemetry-propagator-jaeger	16s
opentelemetry-exporter-zipkin-json	18s
opentelemetry-exporter-otlp-proto-http	22s
opentelemetry-test-utils	21s
opentelemetry-exporter-opencensus	18s
opentelemetry-exporter-prometheus	23s
opentelemetry-exporter-otlp-proto-grpc-latest	19s
opentelemetry-exporter-otlp-combined	20s
opentelemetry-opencensus-shim	16s
opentelemetry-propagator-b3	19s
	6m 28s

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