[FEATURE]: Introduce Common Message Format for plugins

[araujof]

Description

Implement the initial revision of the a Common Message Format (CMF) that defines a provider-agnostic, structured representation for interactions between users, agents, tools, and language models.

CMF provides a canonical message model that supports interoperability, policy enforcement, access control, data governance, and end-to-end auditing across heterogeneous model providers and agent frameworks.