Database setup for the Website service (#13)

This PR contains the work done to introduce a _Fluent_-based persistence layer for the Website service, selectable at runtime alongside the existing in-memory default, plus the local dev tooling and docs to support it.

To provide further details about the work:

* Persistence package
  * The `Driver` and `TLS` enumerations
  * The `Configuration` type
  * The `Service` factory that builds the  service
  * `PrepareDB` for migrations registration
  * The `Probe` for readiness checks.

* App integration
  *  Builds the driver, registers migrations, and attaches `Fluent` to the service lifecycle so it starts/stops with the HTTP server.
  * Migrate-on-boot is gated to the in-memory backend; MySQL/MariaDB is migrated out of band via --database-migrate so shared databases never race on startup.
  * The `ConfigReader+Properties` extension maps database.* config keys onto the driver.

* Library
  * Added database configuration constants.
  * The `HealthController` controller gains a readiness probe: `GET /health/ready` checks whether the database is reachable, separate from the existing liveness check.

* Others
  * Updated the `docker-compose` files to support a database service behind a database profile, and hardened for local development
  * New database targets on the `Makefile` file and overall documentation updated
  * Updated the `.env.local`, `Dockerfile`, and `README` files to document the persistence workflow, config keys, and local DB commands

Reviewed-on: rock-n-code/loud-amsterdam#13
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>
Co-committed-by: Javier Cicchelli <javier@rock-n-code.com>

Services/Website/Sources/Library/Public/Extensions/String+Constants.swift

@@ -1,4 +1,23 @@
 extension String {
+    /// A namespace for the persistence's default configuration values and recognized tokens.
+    public enum Database {
+        /// The default persistence driver: in-memory SQLite, which needs no external infrastructure.
+        public static let driver = "inMemory"
+        /// The driver token selecting the MySQL/MariaDB backend.
+        public static let driverMySQL = "mysql"
+        /// The default MySQL/MariaDB host.
+        public static let host = "localhost"
+        /// The default database name.
+        public static let name = "loud"
+        /// The default database username.
+        public static let username = "loud"
+        /// The default TLS posture token.
+        public static let tls = "prefer"
+        /// The TLS token disabling TLS.
+        public static let tlsOff = "off"
+        /// The TLS token requiring TLS.
+        public static let tlsRequire = "require"
+    }
     /// A namespace for well-known path string constants.
     public enum Path {
         /// The directory, relative to the working directory, that the website's static files are served from.