feat: Add support for _meta across fields defined in MCPSchema

[pantanurag555]

_meta field was added to multiple fields in the schema to make it easy to pass metadata when communicating between an MCP client and server. Relevant spec PR: modelcontextprotocol/modelcontextprotocol#710

Relevant documentation: https://modelcontextprotocol.io/specification/2025-06-18/basic#meta

I am working on changes to add it for all fields in java-sdk. Creating an issue to avoid duplicated work.