Handle no infra/account/*.tfbackend files better for initial setup

Rather than erroring on a project with no `infra/account/*.tfbackend`
files, have `bin/accounts-ids-by-name` return a valid but empty JSON
object. This is more predictable behavior and allows Terraform to error
on the specific lookup locations rather than when the script is
triggered (which also avoids having to conditionally execute the script,
etc.).

Author: doshitan

bin/account-ids-by-name

@@ -8,7 +8,7 @@ set -euo pipefail
 script_dir=$(dirname "$0")
 
 key_value_pairs=()
-backend_config_file_paths=$(ls -1 "${script_dir}"/../infra/accounts/*.*.tfbackend)
+backend_config_file_paths=$(ls -1 "${script_dir}"/../infra/accounts/*.*.tfbackend 2> /dev/null || true)
 
 for backend_config_file_path in $backend_config_file_paths; do
   backend_config_file=$(basename "$backend_config_file_path")