Make runtime manifest log output debug messages

[carolynvs]

What does this change

We shouldn't always be printing out log lines when executing the runtime manifest. Those were always intended to be debug lines and I just missed gating them with a Debug check.

This makes sure that they are only printed when --debug is speciifed and that they are printed to stderr.

What issue does it fix

I was running simple bundles and copying the output for our documentation and realize we are printing at the wrong level.

Notes for the reviewer

N/A

Checklist

• Did you write tests?
• Did you write documentation?
• Did you change porter.yaml or a storage document record? Update the corresponding schema file.
• If this is your first pull request, please add your name to the bottom of our Contributors list. Thank you for making Porter better! 🙇‍♀️

Reviewer Checklist

• Comment with /azp run test-porter-release if a magefile or build script was modified
• Comment with /azp run porter-integration if it's a non-trivial PR

[carolynvs]

/azp run porter-integration

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