Suggestion: provide examples in docs for how to push changes to enums across subgraphs (and avoid composition errors)

specifically this scenario: https://github.com/apollographql/federation/blame/ba3175ec0fe450bdb3902b4893ff75c4f782d8b3/docs/source/schema-design/federated-schemas/reference/composition-rules.mdx#L442

it's unclear to readers how they would add a new enum without breaking composition. is there something we can link to?

Start with the enum guidance around line 442 of docs/source/schema-design/federated-schemas/reference/composition-rules.mdx and review the linked blame context. Add a clear example or link explaining how to introduce enum values across subgraphs without composition errors; the documentation is done when readers can follow the scenario safely.

Written by the indexing model from the issue text.