No longer attach outgoing headers in OTel propagators if there's no URL #5725

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.