Allow changes to amount of spaces for formatting package.json

[josephliccini]

We are using beachball, and our team uses 4 spaces instead of 2 spaces for formatting our package.json files.

When Beachball bump runs, it adjusts this to a hardcoded amount of spaces (2): https://github.com/microsoft/beachball/blob/4d865c83ce4634c8e455268f10f3d8cc950872fd/packages/beachball/src/bump/performBump.ts#L29

Could we allow this to be user-configured?