add migration guide, add protections and migration assistance

docs/strategy_migration.md

@@ -728,3 +728,77 @@ Targets now get their own, dedicated method.
 
         return dataframe
 ```
+
+
+### FreqAI - New data Pipeline
+
+If you have created your own custom `IFreqaiModel` with a custom `train()`/`predict()` function, *and* you still rely on `data_cleaning_train/predict()`, then you will need to migrate to the new pipeline. If your model does *not* rely on `data_cleaning_train/predict()`, then you do not need to worry about this migration. That means that this migration guide is relevant for a very small percentage of power-users. If you stumbled upon this guide by mistake, feel free to inquire in depth about your problem in the Freqtrade discord server.
+
+The conversion involves first removing `data_cleaning_train/predict()` and replacing them with a `define_data_pipeline()` and `define_label_pipeline()` function to your `IFreqaiModel` class:
+
+```python  linenums="1" hl_lines="10-13 41-42 48-49"
+class MyCoolFreqaiModel(BaseRegressionModel):
+    """
+    Some cool custom IFreqaiModel you made before Freqtrade version 2023.6
+    """
+    def train(
+        self, unfiltered_df: DataFrame, pair: str, dk: FreqaiDataKitchen, **kwargs
+    ) -> Any:
+
+        # ... your custom stuff
+
+        # Remove these lines
+        # data_dictionary = dk.make_train_test_datasets(features_filtered, labels_filtered)
+        # self.data_cleaning_train(dk)
+        # data_dictionary = dk.normalize_data(data_dictionary)
+
+        # Add these lines. Now we control the pipeline fit/transform ourselves
+        dd = dk.make_train_test_datasets(features_filtered, labels_filtered)
+        dk.feature_pipeline = self.define_data_pipeline(threads=dk.thread_count)
+        dk.label_pipeline = self.define_label_pipeline(threads=dk.thread_count)
+
+        (dd["train_features"],
+         dd["train_labels"],
+         dd["train_weights"]) = dk.feature_pipeline.fit_transform(dd["train_features"],
+                                                                  dd["train_labels"],
+                                                                  dd["train_weights"])
+
+        (dd["test_features"],
+         dd["test_labels"],
+         dd["test_weights"]) = dk.feature_pipeline.transform(dd["test_features"],
+                                                             dd["test_labels"],
+                                                             dd["test_weights"])
+
+        dd["train_labels"], _, _ = dk.label_pipeline.fit_transform(dd["train_labels"])
+        dd["test_labels"], _, _ = dk.label_pipeline.transform(dd["test_labels"])
+
+    def predict(
+        self, unfiltered_df: DataFrame, dk: FreqaiDataKitchen, **kwargs
+    ) -> Tuple[DataFrame, npt.NDArray[np.int_]]: # 37
+
+        # ... your custom stuff
+
+        # Remove these lines:
+        # self.data_cleaning_predict(dk)
+
+        # Add these lines:
+        dk.data_dictionary["prediction_features"], outliers, _ = dk.feature_pipeline.transform(
+            dk.data_dictionary["prediction_features"], outlier_check=True)
+
+        # Remove this line
+        # pred_df = dk.denormalize_labels_from_metadata(pred_df)
+
+        # Replace with these lines
+        pred_df, _, _ = dk.label_pipeline.inverse_transform(pred_df)
+        if self.freqai_info.get("DI_threshold", 0) > 0:
+            dk.DI_values = dk.feature_pipeline["di"].di_values
+        else:
+            dk.DI_values = np.zeros(len(outliers.index))
+        dk.do_predict = outliers.to_numpy()
+```
+
+
+1. Features - Move to `feature_engineering_expand_all`
+2. Basic features, not expanded across `include_periods_candles` - move to`feature_engineering_expand_basic()`.
+3. Standard features which should not be expanded - move to `feature_engineering_standard()`.
+4. Targets - Move this part to `set_freqai_targets()`.