Deprecation Guide for Deprecate Promise Many Array Behaviors

Deprecates errorsHashToArray errorsArrayToHash and normalizeModelName.

Users making use of these (already private) utilities can trivially copy them into their own codebase to continue using them, though we recommend refactoring to a more direct conversion into the expected errors format for the errors helpers.

For refactoring normalizeModelName we also recommend following the guidance in RFC#740 Deprecate Non-Strict Types.