Refactor: Rename DocumentOperator to DocumentService

Updated project and solution files to rename and restructure
`DocumentOperator` to `DocumentService`. Modified project
references in `DocumentService.API.csproj`, `DocumentService.Application.csproj`,
and `DocumentService.Infrastructure.csproj` to reflect the new
naming convention. Updated `DocumentService.sln` to remove
old project references, add new ones, and adjust configuration
and nested project mappings accordingly. This change aligns
the project structure with the new naming convention.

DocumentService.API/appsettings.Development.json

@@ -0,0 +1,16 @@
+{
+  "Serilog": {
+    "MinimumLevel": {
+      "Default": "Debug"
+    }
+  },
+
+  "DocumentServiceSettings": {
+    "TempFolderPath": "C:\\Temp\\DocumentService\\Dev",
+    "EnableDetailedLogging": true
+  },
+
+  "RedisSettings": {
+    "ConnectionString": "localhost:6379"
+  }
+}