Support multiple Log Analytics workspaces in the same run

[bittrance]

Technically speaking, it is easy to add LogSource objects different workspaces, but the current CLI arg style has no way to tell which args concerns a certain workspace. The tables may not even exist in that workspace, causing query failures. We either need a different arg style or we need to ignore certain kinds of failures when running with multiple workspaces, resulting in fiddly "It's ok for either to fail, but not both."