feat: add structured logging support with severity levels

- Add client and server-side logging capabilities with configurable severity levels
- Implement logging message notifications with DEBUG to EMERGENCY levels
- Add logging consumers for client-side log handling
- Update documentation with logging examples and configuration
- Add comprehensive tests for logging functionality
- Fix typo in README.md (notificaiotn -> notification)

- Centralize MCP method names as constants
  - Move all JSON-RPC method names to McpSchema class as static constants
  - Replace hardcoded method strings with constant references in McpAsyncClient
    and McpAsyncServer
  - Update test cases to use new method name constants

Resolves #35

mcp/src/main/java/org/springframework/ai/mcp/server/McpSyncServer.java

@@ -16,9 +16,12 @@
 
 package org.springframework.ai.mcp.server;
 
+import reactor.core.publisher.Mono;
+
 import org.springframework.ai.mcp.server.McpServer.PromptRegistration;
 import org.springframework.ai.mcp.server.McpServer.ResourceRegistration;
 import org.springframework.ai.mcp.server.McpServer.ToolRegistration;
+import org.springframework.ai.mcp.spec.McpSchema.LoggingMessageNotification;
 import org.springframework.ai.mcp.util.Assert;
 
 /**
@@ -113,6 +116,14 @@ public class McpSyncServer {
 		this.asyncServer.notifyPromptsListChanged().block();
 	}
 
+	/**
+	 * Send a logging message notification to all clients.
+	 * @param loggingMessageNotification The logging message notification to send
+	 */
+	public void loggingNotification(LoggingMessageNotification loggingMessageNotification) {
+		this.asyncServer.loggingNotification(loggingMessageNotification).block();
+	}
+
 	/**
 	 * Close the server gracefully.
 	 */