Fix invalid import paths under "Getting Started" #4319

Job	Run time
lint	3m 50s
external-types (opentelemetry)	1m 1s
test (stable)	6m 33s
external-types (opentelemetry-sdk)	1m 12s
test (beta)	15m 16s
cargo-deny	27s
docs	1m 29s
msrv	4m 44s
non-default-examples (opentelemetry-otlp/examples/basic-otlp)	1m 2s
coverage	3m 41s
	39m 15s

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