[RULE 1041] AddedPropertyInResponse shoul suggest adding "readonly true"

"Adding optional property in response" will cause SDK breaking changes only in case of GET-PUT. It's possible to avoid such scenario if the property is marked as "read only = true". The error/warning message should suggest adding it.

Start with the implementation of RULE 1041, AddedPropertyInResponse, and locate where its error or warning message is assembled. Update the diagnostic so it suggests marking the added response property as read-only, then verify the message using the repository's existing rule or command-line checks.

索引モデルが issue の本文から書いたものです。