docs: Add viztracer command for testing targets

[mjsqu]

When it comes to testing targets it took me a long while to work out I could use the --input switch to pass a file of records to the target rather than trying to work out how to run viztracer on a command containing a pipe 🤯. If the added line can be proven to work by a reviewer and it's OK to be added to the documentation then it would have saved me heaps of time yesterday 😄

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📚 Documentation preview 📚: https://meltano-sdk--1925.org.readthedocs.build/en/1925/

[mjsqu]

I also had some success by restricting the output of the command using --include_files - the full command I was running:

poetry run viztracer --include_files ${HOME}/.cache/pypoetry/virtualenvs/meltanolabs-target-snowflake* -o results.html -- target-snowflake --config=ENV --input=messages.json

[edgarrmondragon]

If the added line can be proven to work by a reviewer

Confirmed 🙂

Thanks @mjsqu!