Description:
Allow specifying a way to only update patches, e.g. from 6.0.200 to 6.0.201 but not to 6.0.300.
Either using an option like the global json (rollForward: latestPatch), or using the 6.0.2xx specification.

Justification:
Some .NET SDK updates, e.g. from 6.0.200 to 6.0.300 cause compile errors due to small changes in compiler or nuget tools.

Are you willing to submit a PR?
Yes, if proposal is accepted.