Add `defaultConfigStderr` for tracing to stderr

[eyeinsky]

(Haven't been able to figure out why running nix-shell doesn't work, get this error:

building '/nix/store/bb729yclf297zin94f7fmsmww2a391f3-git-ls-files.drv'...
error:
       … in the left operand of the update (//) operator

         at /home/user/src/iohk-monitoring-framework/shell.nix:66:8:

           65|
           66|  shell // { inherit devops; }
             |        ^
           67|

       … in the left operand of the update (//) operator

         at /nix/store/pchwfifqmjbq5bwmlbli5l9w3h299hx5-haskell.nix-src/overlays/haskell.nix:780:25:

          779|         cabalProject = args: let p = cabalProject' args;
          780|             in p.hsPkgs // p;
             |                         ^
          781|

       (stack trace truncated; use '--show-trace' to show the full trace)

       error: Index state found was  and no `index-sha256` was provided.

)

checklist

• [ ] compiles (cabal v2-build or stack build)
• [ ] tests run successfully (cabal v2-test or stack test)
• [ ] documentation added
• [ ] link to an issue
• [ ] add milestone (the current sprint)