[SPIKE] Check for possible client_sampled in tagging

[iambriccardo]

Right now the error tagging doesn't support client side sampling, that is, if a trace is sampled out by the head of the trace, this information is not propagated in the trace header (aka dsc). This means that from the perspective of dynamic sampling, we don't know whether the trace has been sampled out on the client and this could lead to false positives.

We would need to fix this by having the client SDKs add the client sampling decision in the dsc that will be attached to the error. This client sampling decision will work similarly to dynamic sampling, that is, if the head is sampled out all the children are sampled out and vice versa.

[ale-cota]

Waiting for SDK work and overall tracking issue.

[iambriccardo]

Had a meeting with @sl0thentr0py @smeubank @cleptric @jan-auer and we agreed that the SDKs team will drive the effort to add the sampled field in the DSC and Relay will take that in consideration when performing tagging.