feat(tools/hash-password): Add a wrapper script for slappasswd

This wrapper script correctly invokes slappasswd for generating ARGON2
hashes.

People without Nix will need to figure this out on their own.

Change-Id: I264715ba4932855b868bef70cc9102515b3d129e
Reviewed-on: https://cl.tvl.fyi/c/depot/+/833
Tested-by: BuildkiteCI
Reviewed-by: BuildkiteCI
Reviewed-by: Kane York <rikingcoding@gmail.com>

bin/__dispatch.sh

@@ -49,6 +49,9 @@ case "${TARGET_TOOL}" in
   gerrit)
     attr="tools.gerrit-cli"
     ;;
+  hash-password)
+    attr="tools.hash-password"
+    ;;
   *)
     echo "The tool '${TARGET_TOOL}' is currently not installed in this repository."
     exit 1