Allow customizing CKRecord.Reference action

Right now `CKRecord.Reference`'s action is hardcoded to `.deleteSelf`
https://github.com/olmps/NestedCloudKitCodable/blob/2c33db6dd6f01f7ef06e7b72cdcdf8d7fbda5073/Source/Classes/Encoder/CKEncoderKeyedContainer.swift#L203
Can we pass an option to `CKRecordEncoder` to customize this value to either `.deleteSelf` or `.none`? Thanks