Add Bill of Materials (BOM) for dependency management

Introduces a new mcp-bom module to simplify dependency version management across
Spring AI MCP projects. The BOM allows users to import a single dependency that
manages versions of all MCP components, ensuring version compatibility and reducing
maintenance overhead.

- Adds mcp-bom module with managed versions for all Spring AI MCP dependencies
- Provides centralized version control through a single BOM import
- Removes explicit version declarations from documentation examples
- Adds dependency management documentation and updates existing docs to reference the new BOM

Resolves #59