Summary

When type_name_overrides is used to collapse input enum names onto output enum names (e.g., "ColorInput" => "Color"), the standard 3-stage enum value migration becomes impossible — removing the override simultaneously renames all filter field types, breaking all clients at once with no transition period.

This PR adds an enums_in_transition configuration option that enables gradual migration:

• Generates a transition *Input enum type alongside the collapsed output enum
• Adds an equalToAnyOfInput filter field that accepts the new input enum type
• Processes equalToAnyOfInput identically to equalToAnyOf at runtime (same ES terms query, same null handling, same shard routing optimization)
• Validates that enums_in_transition names match defined enum types, with DidYouMean suggestions

Migration workflow this enables

1. Add enum to enums_in_transition — schema gains ColorInput enum and equalToAnyOfInput filter field
2. Clients migrate from equalToAnyOf: [Color] to equalToAnyOfInput: [ColorInput] at their own pace
3. Remove the type_name_overrides entry — equalToAnyOf now naturally uses [ColorInput]
4. Clients migrate back to equalToAnyOf (or keep using equalToAnyOfInput as a permanent alias)
5. Remove enum from enums_in_transition

Key mechanisms

• skip_name_override on EnumType constructor — bypasses type_name_overrides for transition input enum creation
• type_already_final on Field — bypasses to_final_form for filter field type resolution
• Shared lambda in FilterNodeInterpreter for both equalToAnyOf and equalToAnyOfInput
• RoutingPicker, IndexExpressionBuilder, and Filters all handle the new operator for shard routing and index pruning
• Apollo and Warehouse factory extensions forward **kwargs so skip_name_override reaches the base method
• All RBS type signatures updated for new parameters and methods

Test plan

• All existing elasticgraph-schema_definition unit tests pass (1620 examples)
• All existing elasticgraph-graphql unit tests pass (1336 examples)
• All existing elasticgraph-schema_artifacts unit tests pass (105 examples)
• New tests verify transition input enum generation with type_name_overrides active
• New tests verify equalToAnyOfInput filter field on both standard and list element filter types
• New tests verify no transition types generated when enum is not in enums_in_transition
• Tests run with both camelCase and snake_case casing forms
• Integration tests with a running datastore (pending)