[otap-dataflow] add transport header infrastructure

[c1ly]

Change Summary

Update the OtapPdata Context with the transport_headers field, so that OtapPdata can carry the headers through the pipeline.

Defined the TransportHeadersPolicy with HeaderCapturePolicy and HeaderPropagationPolicy, update the Policies to have a transport_headers field. Receiver and Exporter nodes can also define HeaderCapturePolicy and HeaderPropagationPolicy respectively, these definitions will override any top level HeaderCapturePolicy and HeaderPropagationPolicy rules.

Exposed the policy to the Receiver and Exporter nodes via the EffectHandler with helper functions that apply the policies on a iterator of key value pairs (for receiver nodes) and transport_headers (for exporter nodes)

What issue does this PR close?

• Closes Support policy-based transport header extraction and propagation in OtapPdata #2508

How are these changes tested?

unit tests and integration tests

Are there any user-facing changes?

no

[albertlockett]

I wonder if the signature of this method should return some feedback about whether we failed to consume some of the pairs? Otherwise, it becomes a bit cumbersome, because we'd need to check a) that the pairs iter was consumed and b) that the result length is equal to the iter that was passed.

Maybe a different signature could be something like:

    pub fn capture_from_pairs<'a>(
        &self,
        headers: &mut TransportHeaders
        pairs: impl Iterator<Item = (&'a str, &'a [u8])>,
    ) -> Result<()> {