debuginfo/symbolizer: Decouple symbolization from debuginfo component

[brancz]

The debuginfo component is currently doing the actual symbolization, while the symbolizer really just handles the interaction with the metastore. This should be decoupled for a better separation of concerns.

I would propose to add download functionality to the debuginfo component, which the symbolized utilizes to get the debuginfos it cares about for a particular case of symbolizing.