Refactor MCP clients to use the boto3 API instead of manually signing SigV4 requests

Customers are using this sample as a reference point for implementing MCP servers

Currently, our primary tutorials (01-Tutorials, 01-AgentCore Runtime, 02-Hosting an MCP server) use manual Sigv4 signing as the reference implementation.

This creates a significant barrier to entry. Customers using this sample as a reference point are also manually signing Sigv4 requests, which is increasing their code maintenance burden and slowing down their integration time.

Since the boto3 API now supports AgentCore Runtime natively, the sample can be updated to use boto3 as the default. This will eliminate the learning curve associated with manual signing, significantly reduce customer boilerplate code, and accelerate the adoption of MCP servers on Agentcore runtime

Start by reviewing the MCP client examples in 01-Tutorials, 01-AgentCore Runtime, and 02-Hosting an MCP server, identifying where manual SigV4 signing is used. Compare those paths with the boto3 AgentCore Runtime API, then verify that the tutorials consistently use boto3 as the default reference implementation.

Written by the indexing model from the issue text.