Ensure dependency on yarn info is optional

[finn-orsini]

What

This utility internally relies on the output of yarn info for the default getPackageVersionInfo argument.

The default arguments are not documented, and it is unclear if they are available for the public API or only internal methods.

Ensure that:

• Consumers can easily override the function which fetches package version info
• The expected return format of that function is specified and decoupled from yarn info, which may require changes to the current setup

Why

This package was initially written for gathering metrics for npm packages, but the metrics apply to any semver versioned library. For other language packages, or those whos info is not available via the info command - this package should be able to accept version information and calculate the specified metrics.