[Bug]: patch releases for the spec repo should only be for non-functional changes

As discussed in the TSC call, patch releases for the spec repo should only be for non-functional changes to the spec text / comments in the proto etc. As soon as functional changes to the a2a.proto are made this requires a minor release. Do we need to put this in the spec somewhere?

_Originally posted by @Tehsmash in https://github.com/a2aproject/A2A/pull/1259#discussion_r2665695152_

Find where release policies or versioning guidelines are documented in the spec repository, likely in a README, CONTRIBUTING, or versioning document. Understand the difference between patch and minor releases as referenced in the linked PR discussion. The task is to add a clarifying statement that functional changes to a2a.proto necessitate a minor release, while patch releases are for non-functional changes only.

Scritto dal modello di indicizzazione a partire dal testo della issue.