Feat/tz aware dta

[dennisbader]

fixes #2000.

Summary

• adds support for time index time zone conversion with parameter tz before generating/computing holidays and datetime attributes.
  • darts.utils.timeseries_generation.datetime_attribute_timeseries
  • darts.utils.timeseries_generation.holidays_timeseries
  • all time axis encoders and add_encoders dict for automatic encoders in forecasting models
  • darts.Timeseries.add_holidays
    - darts.Timeseries.add_datetime_attribute

[codecov-commenter]

Codecov Report

All modified and coverable lines are covered by tests ✅

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Files	Coverage Δ
darts/dataprocessing/encoders/encoders.py	97.68% <100.00%> (+0.07%)	⬆️
darts/models/forecasting/arima.py	93.75% <ø> (ø)
darts/models/forecasting/auto_arima.py	96.77% <ø> (ø)
darts/models/forecasting/block_rnn_model.py	98.27% <ø> (-0.03%)	⬇️
darts/models/forecasting/catboost_model.py	98.41% <ø> (ø)
darts/models/forecasting/croston.py	90.69% <ø> (ø)
darts/models/forecasting/dlinear.py	99.12% <ø> (ø)
darts/models/forecasting/kalman_forecaster.py	97.36% <ø> (ø)
darts/models/forecasting/lgbm.py	100.00% <ø> (ø)
...arts/models/forecasting/linear_regression_model.py	94.44% <ø> (ø)
... and 18 more

... and 2 files with indirect coverage changes

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[madtoinou]

Nice! Just a few typo here and there.