[vcpkg] Add an option ADD_TO_PATH in vcpkg_find_acquire_program

Simple as the title says: I would like to see an option `ADD_TO_PATH` in `vcpkg_find_acquire_prorgram` since a lot of build scripts require the tools to be on the `PATH`. This gets rid of the necessary code to extract the path from the cmake variable set by `vcpkg_find_acquire_program` and the additional code to transform it into the native form and then adding it to the `PATH` variable.