Build retention tool should verify symbols were archived for inserted builds

Right now we kick off archiving for inserted builds. But if that job fails, or nobody ever ran the insertion tool (and it was inserted manually), we won't try again. The retention tool already has what's needed to do this, so we should just update it to check too.

Start by reading the retention tool and the existing build insertion and archiving flow. Trace how inserted builds trigger symbol archiving and identify the existing retention checks that can be reused. Done means the retention tool also detects builds whose symbols were not archived and attempts archiving again, including manually inserted builds.

Written by the indexing model from the issue text.