Allow unsignedPluginAllowList.json in a Salesforce DX Project Structure

[mcarvin8]

Per https://developer.salesforce.com/docs/atlas.en-us.sfdx_setup.meta/sfdx_setup/sfdx_setup_allowlist.htm#maincontent, you can add a unsignedPluginAllowList.json to install unsigned plugins automatically for a specific User.

It would be nice to allow this JSON file to exist in a Salesforce DX project structure (in the config folder perhaps) so that anyone who works in the same project can install recommended unsigned plugins without being prompted. This also would be useful for CI/CD builds that use unsigned plugins.