Windows support (agent) (#212)

* Create stubs for non-windows code

* Disable dotnet profiling options for Windows

* Implement windows-specific parts

* Fix configuration type

* Add MSI package definition

* Embed windows version info at build

* Add agent run mode

* Rework windows-dev build

* Add target manager

* Rework CLI

* Allow pyroscope agent to run without a config file

* Rework agent logging

* Improve error messages

Co-authored-by: Dmitry Filimonov <dmitry@pyroscope.io>