• backport: otel: Avoid excessive memory allocations if not configured #49078

• fixes: Memory leak #49075

• relates to Make log reading more robust to errors #47983

Use noop tracer provider if the OTEL exporter is not configured. This makes the OTEL tracing avoid doing unneeded memory allocations for spans which aren't going to be exported anywhere anyway.

- How to verify it

#!/bin/sh

docker run -d --rm -it --name leak alpine sh -c 'while true; do date; done'

for i in $(seq 0 4); do
    docker logs -f leak >/dev/null &
done


watch -d ps -C dockerd -o rss=

docker rm -f leak

wait

Before this patch, the RSS grows significantly over time, in proportion to the amount of running docker logs -f.
After the patch, the RSS stays around the same level.

- Description for the changelog

Fix excessive memory allocations when OTEL is not configured.

- A picture of a cute animal (not mandatory but encouraged)