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.json

@@ -5,5 +5,62 @@
       "Microsoft.AspNetCore": "Warning"
     }
   },
-  "AllowedHosts": "*"
-}
+  "AllowedHosts": "*",
+
+  "Serilog": {
+    "MinimumLevel": {
+      "Default": "Information",
+      "Override": {
+        "Microsoft": "Warning",
+        "Microsoft.AspNetCore": "Warning",
+        "System": "Warning"
+      }
+    },
+    "WriteTo": [
+      {
+        "Name": "Console",
+        "Args": {
+          "outputTemplate": "[{Timestamp:HH:mm:ss} {Level:u3}] {Message:lj} {Properties:j}{NewLine}{Exception}"
+        }
+      },
+      {
+        "Name": "File",
+        "Args": {
+          "path": "Logs/log-.txt",
+          "rollingInterval": "Day",
+          "outputTemplate": "{Timestamp:yyyy-MM-dd HH:mm:ss.fff zzz} [{Level:u3}] {Message:lj} {Properties:j}{NewLine}{Exception}"
+        }
+      }
+    ],
+    "Enrich": [ "FromLogContext", "WithMachineName", "WithThreadId" ]
+  },
+
+  "DocumentOperatorSettings": {
+    "TempFolderPath": "C:\\Temp\\DocumentOperator",
+    "TempFileRetentionHours": 24,
+    "MaxPdfSizeMB": 50,
+    "EnableDetailedLogging": true
+  },
+
+  "RedisSettings": {
+    "ConnectionString": "localhost:6379",
+    "InstanceName": "DocumentOperator:",
+    "CacheExpirationMinutes": 60
+  },
+
+  "ApiKeySettings": {
+    "EnableValidation": true,
+    "Keys": {
+      "customer-a-key-12345": {
+        "TenantId": "customer-a",
+        "TenantName": "Customer A GmbH",
+        "IsActive": true
+      },
+      "customer-b-key-67890": {
+        "TenantId": "customer-b",
+        "TenantName": "Customer B AG",
+        "IsActive": true
+      }
+    }
+  }
+}