Update package.json and add prettierignore

[benbridts]

Description of changes:

• Our build pipeline (using nodejs20) complained about old node versions in package.json, I've update the ones I could find
• locally I frequently had to run prettier to get unit tests to pass, ignoring the build outputs makes sense
• this also includes the commit from https://github.com/aws-solutions/distributed-load-testing-on-aws/pull/178, otherwise unit tests don't pass

Checklist

• [X] :wave: I have run the unit tests, and all unit tests have passed.
• [X] :warning: This pull request might incur a breaking change.

Breaking is very unlikely, but I have not tested this on older node build environments

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