Release otap-dataflow on crates.io

[jmacd]

It would be convenient for users at this point, I think, to have crates released on crates.io that they can kick around.

See related issue #737

[jmacd]

I discussed prerequisites with @lquerel. As a primary blocker, we need to integrate and rationalize the layout of our otap-dataflow crates. The otel-arrow-rust sibling crate will have to move in a coherent way into otap-dataflow/crates/pdata.