Ease restriction on inserting earlier builds

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?

No source files, tests, or entry points are named. Start with the insertion tool's handling of build age relative to the base branch, then inspect the linked Azure DevOps release logs for the failing scenario. Done means an older-numbered build can be inserted when it represents newer source, with the existing restriction removed or revised safely.

Written by the indexing model from the issue text.