refactor(users/glittershark): Rename to grfn

Rename my //users directory and all places that refer to glittershark to
grfn, including nix references and documentation.

This may require some extra attention inside of gerrit's database after
it lands to allow me to actually push things.

Change-Id: I4728b7ec2c60024392c1c1fa6e0d4a59b3e266fa
Reviewed-on: https://cl.tvl.fyi/c/depot/+/2933
Tested-by: BuildkiteCI
Reviewed-by: tazjin <mail@tazj.in>
Reviewed-by: lukegb <lukegb@tvl.fyi>
Reviewed-by: glittershark <grfn@gws.fyi>

users/grfn/xanthous/.github/actions/nix-build/entrypoint.sh

@@ -0,0 +1,24 @@
+#!/usr/bin/env bash
+
+# Entrypoint that runs nix-build and, optionally, copies Docker image tarballs
+# to real files. The reason this is necessary is because once a Nix container
+# exits, you must copy out the artifacts to the working directory before exit.
+
+[ "$DEBUG" = "1" ] && set -x
+[ "$QUIET" = "1" ] && QUIET_ARG="-Q"
+
+set -e
+
+# file to build (e.g. release.nix)
+file="$1"
+
+[ "$file" = "" ] && echo "No .nix file to build specified!" && exit 1
+[ ! -e "$file" ] && echo "File $file not exist!" && exit 1
+
+echo "Building all attrs in $file..."
+nix-build --no-link ${QUIET_ARG} "$file" "${@:2}"
+
+echo "Copying build closure to $(pwd)/store..."
+mapfile -t storePaths < <(nix-build ${QUIET_ARG} --no-link "$file" | grep -v cache-deps)
+printf '%s\n' "${storePaths[@]}" > store.roots
+nix copy --to "file://$(pwd)/store" "${storePaths[@]}"