Send the opentracing span information also to appservices

[MTRNord]

This fixes #16226

The intent here is that appservice developers also may be interested to link their traces to the synapse traces. It's treated like the replication traces, since appservices are being run by the same admin. So there is no need to whitelist each appservice domain.

Pull Request Checklist

• [x] Pull request is based on the develop branch
• [x] Pull request includes a changelog file. The entry should:
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Signed-off-by: Marcel Radzio support@nordgedanken.dev

[MTRNord]

I am not sure if there is a cleaner way to do this. The underlying HTTP client is shared with other parts of the code, so in my head it made sense to do it just on the appservice code side. If this is not correct, I would need some guidance on a better way to archive a better solution.

[MTRNord]

Test failures are noted and being worked on.

Tests should be fixed