Change default output directory for Frosting to repository root

`Cake.Frosting.Issues.Recipe` expects to run in a sub directory of the project and have the build directory set as working directory (`BuildRootDirectory``= `./`, `ProjectRootDirectory` = `../`).

Output directory for Cake.Frosting.Issues.Recipe is currently `BuildArtifacts` relative to the working directory which will result in a sub directory `BuildArtifacts` below the build directory and not the project directory.

Start at Cake.Frosting.Issues.Recipe and trace how BuildArtifacts is resolved when BuildRootDirectory is ./ and ProjectRootDirectory is ../. Confirm the output path is based on the repository root rather than the build directory; done when generated artifacts appear in the repository's BuildArtifacts directory.

Written by the indexing model from the issue text.