Fix alstm models and the corresponding yaml documents

[hellowordma]

Description

To make it possible to pass parameter of rnn_type. Otherwise, whatever rnn_type you choose, the code will adopt the default type --GRU model. This is an ALSTM model, instead of A-GRU model

Motivation and Context

To make it possible to pass parameter of rnn_type

How Has This Been Tested?

• Pass the test by running: pytest qlib/tests/test_all_pipeline.py under upper directory of qlib.
• If you are adding a new feature, test on your own test scripts.

Screenshots of Test Results (if appropriate):

1. Pipeline test:
2. Your own tests:

Types of changes

• [√] Fix bugs
• Add new feature
• Update documentation

[hellowordma]

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[Fivele-Li]

Hi, I think there are three points that need to be looked at.

1. GRU is also a type of LSTM structure, so it is correct to set "rnn_type: GRU" in the YAML file from this perspective.
2. The "rnn_type" setting in the YAML file was not used, so it is fine to add input parameters to ALSTM. Further more, You can run a test based on the method in README.md, and if the results are better than the current ones, you can replace "GRU" with "LSTM" in the YAML file.
3. Please check the issues reported by Pytest.