Disclose CLI stderr usage

[squakez]

We have not documented this anywhere, so, probably it makes sense to include in the official doc. As we make use of stderr for many CLI warning, this is automatically redirected to stdout to show immediately the result of any error to the user. However, it may be a problem when running dry run operations (ie, -o yaml). We need to show final user how to prevent the error from being logged:

 ./kamel run /tmp/Test.java -o yaml -d camel:test
Warning: dependency camel:test not found in Camel catalog
apiVersion: camel.apache.org/v1
kind: Integration

vs

$ ./kamel run /tmp/Test.java -o yaml -d camel:test 2>/dev/null
apiVersion: camel.apache.org/v1
kind: Integration

[github-actions]

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