Update otel to v0.12.0

[yas-okadatech]

No description provided.

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[bogdandrutu]

A merge and release of this PR would be really appreciated by the opentelemetry-collector-contrib repo

[mrothroc]

It would be great to have this. I'll just note that you can't use go.opentelemetry.io/contrib/instrumentation/google.golang.org/grpc/otelgrpc
to trace gRPC calls in google cloud without this PR because that module requires 0.12.0

[james-bebbington]

LGTM other than one minor comment.

Since this PR is blocking people I will merge it now, but can you please check the comment below and fix in a new PR if correct?

[james-bebbington]

Would this be somewhat cleaner if we returned exporter.Shutdown here instead or exporter.traceExporter.Flush?