feat(mockServer): set preserveResolvers default to true

[cchen9299]

Description

Motivation and Context

https://github.com/americanexpress/parrot/issues/253

How Has This Been Tested?

Tested locally with an OneApp module, but I'm unsure whether sharing screenshots of our local development screens in a public github PR breaches any American Express HR violation. I'm on Web and Mobile Slack!

Types of Changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [x] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [ ] Documentation (adding or updating documentation)
• [ ] Dependency update

Checklist:

• [ ] My change requires a change to the documentation and I have updated the documentation accordingly.
• [x] My changes are in sync with the code style of this project.
• [x] There aren't any other open Pull Requests for the same issue/update.
• [ ] These changes should be applied to a maintenance branch.
• [ ] This change requires cross browser checks.
• [ ] This change impacts caching for client browsers.
• [ ] I have added the Apache 2.0 license header to any new files created.

What is the Impact to Developers Using parrot?

[CLAassistant]

All committers have signed the CLA.