No longer attach outgoing headers in OTel propagators if there's no URL

### Description

Currently we look for a URL on outgoing requests to check against `tracePropagationTargets`. If none can be found in span attributes, we still attach headers. We want to change this to only attach headers if the URL can be found.

This is a breaking change and should land in the next major version.

We also need to check whether there's any cases where there's no URL attributes but the SDK should still attach headers, e.g. for Queue producers and similar things.

Once checked also make sure to update (dev) docs.

Inspect the OpenTelemetry propagator handling for outgoing requests and how tracePropagationTargets is applied when no URL attribute exists. Check queue producers and similar cases for valid URL-less propagation, then update the developer documentation for the breaking change. Done means the intended propagation behavior and documented exceptions are verified.

Written by the indexing model from the issue text.