Replace Logging with Serilog; add new configurations

Replaced the `Logging` configuration in both `appsettings.json`
and `appsettings.Development.json` with Serilog, enabling
structured logging with configurable sinks and enrichment.

Added `DocumentOperatorSettings` to manage temporary files
and logging details. Introduced `RedisSettings` for Redis
integration, including connection string and cache settings.

Added `ApiKeySettings` to support tenant-specific API key
validation with detailed configuration for each tenant.

These changes improve logging, caching, and configuration
management for better maintainability and extensibility.

DocumentOperator.API/appsettings.Development.json

@@ -1,8 +1,16 @@
 {
-  "Logging": {
-    "LogLevel": {
-      "Default": "Information",
-      "Microsoft.AspNetCore": "Warning"
+  "Serilog": {
+    "MinimumLevel": {
+      "Default": "Debug"
     }
+  },
+
+  "DocumentOperatorSettings": {
+    "TempFolderPath": "C:\\Temp\\DocumentOperator\\Dev",
+    "EnableDetailedLogging": true
+  },
+
+  "RedisSettings": {
+    "ConnectionString": "localhost:6379"
   }
-}
+}