Config file changes should minimally bust the cache

[ds300]

We can hash individual parts of the lazy config file when computing the manifest for a task (in computeManifest.js). Rather than busting the whole cache for every change we can be more targeted and only bust the parts that matter. I think we can get away with just hashing the baseCacheConfig and the current task's script config, but part of this ticket is to think deeply about that.

In addition we should also always include a hash of the "scripts" entry string in the manifest, regardless of where it comes from.