18/07/2023 Sparkpost related issues and bug fixes

🎉 New

1. Auto-create Sparkpost sub-account for new Airship accounts. 🧑‍💻James

2. Default all new accounts to send from airshipm2.co.uk 🧑‍💻James

🐛 Bug fix

1. Fixed a bug where an internal email alert exposes the REST API token 🧑‍💻James

2. Fixed a bug where some characters were breaking in the subject line for emails via Sparkpost 🧑‍💻James