…nts and raise error on new segments (#1107)

…1109)

)

)

…or (#1139)

…ble error (#1141)

# Conflicts:
#	.github/workflows/test.yml
#	CHANGELOG.md
#	etna/models/base.py
#	etna/pipeline/base.py
#	etna/pipeline/hierarchical_pipeline.py
#	etna/pipeline/pipeline.py
#	etna/transforms/base.py
#	etna/transforms/encoders/mean_segment_encoder.py
#	etna/transforms/encoders/segment_encoder.py
#	etna/transforms/math/differencing.py
#	etna/transforms/math/sklearn.py
#	etna/transforms/outliers/base.py
#	etna/transforms/timestamp/special_days.py
#	etna/transforms/utils.py
#	tests/test_datasets/test_dataset.py
#	tests/test_models/test_base.py
#	tests/test_models/test_inference/common.py
#	tests/test_models/test_inference/test_forecast.py
#	tests/test_models/test_inference/test_predict.py
#	tests/test_pipeline/test_hierarchical_pipeline.py
#	tests/test_transforms/test_encoders/conftest.py
#	tests/test_transforms/test_encoders/test_mean_segment_encoder_transform.py
#	tests/test_transforms/test_math/test_differencing_transform.py
#	tests/test_transforms/test_math/test_sklearn_transform_interface.py
#	tests/test_transforms/test_outliers/test_outliers_transform.py

# Conflicts:
#	etna/ensembles/direct_ensemble.py
#	etna/ensembles/stacking_ensemble.py
#	etna/ensembles/voting_ensemble.py
#	etna/pipeline/autoregressive_pipeline.py
#	etna/pipeline/base.py
#	etna/pipeline/hierarchical_pipeline.py
#	etna/pipeline/pipeline.py
#	tests/test_ensembles/test_direct_ensemble.py
#	tests/test_ensembles/test_stacking_ensemble.py
#	tests/test_ensembles/test_voting_ensemble.py
#	tests/test_models/test_inference/test_forecast.py
#	tests/test_models/test_inference/test_predict.py
#	tests/test_pipeline/conftest.py
#	tests/test_pipeline/test_autoregressive_pipeline.py
#	tests/test_pipeline/test_hierarchical_pipeline.py
#	tests/test_pipeline/test_pipeline.py
#	tests/utils.py