Add line breakdown API

[kolesnikovae]

We're using pprof query API in order to get breakdown by lines for a specific function. This approach is quite limited (it does not work in sandwich view, and can't be used for e.g., call graphs) and may cause performance issues. See the issue (private) in the app plugin repositry for details.

I propose to add use-case specific API that retrieves per line/location statistics for a given call site or function.