Add tests for installWrangler

[courtney-sims]

Baby step refactor to get more tests into this repo:

• isolates index functions from side effects
• creates type for config
• uses config and package manager types for parameters to index functions so we can pass in some test data
• adds some tests for the InstallWrangler method

Also pins the node version to avoid compatibility issues with the newly released version 23

Tested by running this version on a demo site: