Add docker execution environment

RemoteExec.Server/appsettings.json

@@ -31,7 +31,52 @@
     // Timeout in seconds for loading assemblies from clients
     // If a client doesn't respond with assembly bytes within this time, the request fails
     // Default: 30 seconds
-    "AssemblyLoadTimeoutSeconds": 30
+    "AssemblyLoadTimeoutSeconds": 30,
+    
+    // Type of execution environment to use
+    // Options: "AssemblyLoadContext", "DockerContainer"
+    // - AssemblyLoadContext: Lighter weight, per-connection assembly isolation
+    // - DockerContainer: Maximum isolation, ephemeral containers per task
+    // Default: "AssemblyLoadContext"
+    "ExecutionEnvironment": "AssemblyLoadContext"
+  },
+  
+  // Docker execution configuration (only used when ExecutionEnvironment = "DockerContainer")
+  "DockerExecution": {
+    // Docker host URL
+    // Linux: "unix:///var/run/docker.sock"
+    // Windows: "npipe://./pipe/docker_engine"
+    "DockerHost": "unix:///var/run/docker.sock",
+    
+    // Docker worker image name to use for task execution
+    // Must be built and available on the Docker host
+    // Default: "remoteexec-worker:latest"
+    "WorkerImageName": "remoteexec-worker:latest",
+    
+    // Maximum execution time per container in seconds
+    // Containers exceeding this time will be forcefully terminated
+    // Default: 300 (5 minutes)
+    "ContainerTimeoutSeconds": 300,
+    
+    // Memory limit per container in MB
+    // Prevents containers from consuming excessive memory
+    // Default: 512 MB
+    "ContainerMemoryLimitMb": 512,
+    
+    // CPU shares allocated to each container (relative weight)
+    // Higher values = more CPU priority
+    // Default: 1024
+    "ContainerCpuShares": 1024,
+    
+    // Disable network access in containers for security
+    // Set to false if tasks require network connectivity
+    // Default: true
+    "DisableNetwork": true,
+    
+    // Make container filesystem read-only
+    // Enhances security by preventing file modifications
+    // Default: true
+    "ReadOnlyFilesystem": true
   },
   
   // Server metrics broadcasting configuration