Add stack ghc installation hooks and install stack by default

scripts/hooks/stack/ghc-install.sh

@@ -0,0 +1,21 @@
+#!/bin/bash
+
+# see https://docs.haskellstack.org/en/stable/yaml_configuration/#ghc-installation-customisation-experimental
+# for documentation about hooks
+
+set -euo pipefail
+
+case $HOOK_GHC_TYPE in
+    bindist)
+        echo "$(ghcup run --ghc "$HOOK_GHC_VERSION" --install)/ghc"
+        ;;
+    git)
+        # TODO: should be somewhat possible
+        >&2 echo "Hook doesn't support installing from source"
+        exit 1
+        ;;
+    *)
+        >&2 echo "Unsupported GHC installation type: $HOOK_GHC_TYPE"
+        exit 2
+        ;;
+esac