Add mu4e mail provisioning with vault-backed iCloud secret

scripts/update_protonmail_bridge_secret.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env sh
+
+set -eu
+
+printf "Proton Bridge password: "
+stty -echo
+IFS= read -r proton_bridge_password
+stty echo
+printf "\n"
+
+if [ -z "$proton_bridge_password" ]; then
+  printf "Error: empty password, nothing stored.\n" >&2
+  exit 1
+fi
+
+printf "%s" "$proton_bridge_password" \
+  | secret-tool store --label="ProtonMail Bridge" protonmail-bridge protonmail
+
+printf "ProtonMail Bridge secret updated in GNOME Keyring.\n"