Parallelize collection of logs at each layer of the resource tree walk. Since almost all cost of log collection is at leaf nodes, this should allow the total time for log collection to be close to the time taken for the single longest leaf node, instead of the sum of all leaf nodes.
We need to clear the resource filter during the resource tree walk to ensure that logs from children of matched resources are collected and aggregated.
We have to reverse engineer the name from the soruce LogGroup information since that is all we got at runtime, but luckily that is sufficient given current name generation approach.
This kind of code is *very* sensitive to any changes to automatic name generation - but that is likely inevitable at this layer.
