tornado: reduce cardinality with old semconv metrics attributes (#4666)

* tornado: reduce cardinality with old semconv metrics attributes

Reduce the `http.target` cardinality in metrics when the old semantic
conventions are configured.

* Add changelog

* Apply suggestion from @herin049

Co-authored-by: Lukas Hering <40302054+herin049@users.noreply.github.com>

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Co-authored-by: Lukas Hering <40302054+herin049@users.noreply.github.com>