Add EPP version history to implementers guide with automated maintenance

[zhengkezhou1]

@zhengkezhou1 this is a good start. Can you create a separate issue to add this table to https://gateway-api-inference-extension.sigs.k8s.io/guides/implementers/#callout-extension and tooling that automates the maintenance of the table? We may need to move the EPP proto spec outside of the proposals directory and treat it similarly to API types, e.g. something similar to api-ref-docs to maintain the spec.

Originally posted by @danehans in #1360 (comment)

[zhengkezhou1]

/assign