[DB] Consider introducing `RwLock`

[frisitano]

Overview

We should consider if we need to introduce RwLock to the database such that we only have a single entity performing write operations. This would mean we would modify the database type to be Arc<RwLock<Database>. We currently have database transaction support via the DatabaseTransaction type which provides ACID support and this may be sufficient. As progress on the rollup node develops we consider if we need the application level lock.