add flag to cli freeze command for specifying output file

The current recommend way to capture output from the agentos freeze CLI command is to pipe or redirect STDOUT, using a command like:

agentos/documentation/demos/demo_ilya_papag_from_cli.sh

Line 6 in 14211d9

    
           agentos freeze agent --registry-file $PAPAG_DIR/components.yaml > /tmp/papag-components.yaml

However, with this technique we end up with debugging output in the file we capture (in this case, /tmp/papag-components.yaml). We should add a flag to the agentos freeze command that allows the user to specify the output file to write the frozen registry to.