Ease restriction on inserting earlier builds

[RikkiGibson]

The insertion tool currently fails if you try to insert an "older" build than what is currently present in the base branch.

https://dev.azure.com/devdiv/DevDiv/_releaseProgress?_a=release-environment-logs&releaseId=776275&environmentId=4206948

However, an "older" build may actually represent newer source, such as when you manually queue a build for some earlier commit, then insert it, then go back and try to insert an earlier build that represents a later commit. @JoeRobich @genlu what do you think about removing this restriction?

[genlu]

I think there's a check in VS build that ensures the version number doesn't decrease? Anyway, I think this is fine if the tool can make a comment in the insertion PR saying so, which needs to be manually resolved by someone before merge.

[JoeRobich]

I feel like there could be a flag to override this behavior. Since, most of the time not allowing build numbers to go backwards is the right thing.