Package options should merge recursively

[ecraig12345]

getCombinedPackageOptions should be recursively merging object properties instead of overwriting them (arrays should still be overwritten). Code: https://github.com/microsoft/beachball/tree/ecraig/object-merge

I'm marking this as a breaking change because it's entirely possible that some repos have configs that either expect or manually work around the non-recursive merging behavior, so it's safest to only change this with an explicit call-out in a major release.