(PUP-2943) Add PMT --ignore-changes flag

Prior to this commit there was no way to only ignore local changes to a module.
You had to --force when upgrading/uninstalling, which could potentially have other
repurcussions.
This commit adds the --ignore-changes flag, so a user can specify that they don't
care about local file changes but do not want to force anything else.
I'd really like to see this read the same as / similar to the `upgrade` change.