Add External Type Checking #4406

Job	Run time
lint	4m 9s
external-types (opentelemetry)	59s
test (stable)	7m 2s
external-types (opentelemetry-sdk)	1m 11s
test (beta)	7m 25s
cargo-deny	27s
docs	1m 33s
msrv	4m 49s
external-types (opentelemetry-otlp)	1m 10s
non-default-examples (opentelemetry-otlp/examples/basic-otlp)	42s
external-types (opentelemetry-zipkin)	1m 14s
coverage	3m 15s
	33m 56s

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