Bump go.opentelemetry.io/otel from 1.19.0 to 1.21.0 #811

Job	Run time
govulncheck	1m 17s
setup-environment	26s
unittest-matrix (~1.21.3)	1m 22s
unittest-matrix (~1.20.10)	1m 23s
checks	32s
lint	1m 19s
cross-build-collector (darwin, amd64)	12s
test-coverage	1m 23s
cross-build-collector (darwin, arm64)	8s
cross-build-collector (linux, 386)	8s
cross-build-collector (linux, amd64)	10s
cross-build-collector (linux, arm64)	13s
cross-build-collector (linux, ppc64le)	13s
cross-build-collector (linux, arm, 7)	8s
cross-build-collector (linux, s390x)	12s
cross-build-collector (windows, 386)	13s
cross-build-collector (windows, amd64)	17s
unittest	1s
	9m 37s

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