Enabling to tune hyperparameters for outside models implemented with PyPOTS framework

[WenjieDu]

What does this PR do?

enhance the hyperparameter tuning feature mentioned in #187, and make this feature available for models implemented with PyPOTS framework but not yet included in PyPOTS

Before submitting

• Was this discussed/approved via a GitHub issue? Please add a link to it if that's the case.
• I have commented my code, particularly in hard-to-understand areas.
• I have written necessary tests and already run them locally.

[coveralls]

Pull Request Test Coverage Report for Build 7219615511

• 0 of 26 (0.0%) changed or added relevant lines in 2 files are covered.
• 3 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.3%) to 82.389%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
pypots/cli/tuning.py	0	13	0.0%
pypots/cli/utils.py	0	13	0.0%

Files with Coverage Reduction	New Missed Lines	%
pypots/cli/tuning.py	3	0.0%

Totals
Change from base Build 7219607015:	-0.3%
Covered Lines:	4842
Relevant Lines:	5877

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💛 - Coveralls

[levisocool]

hello，又是我。想请教下PyPots目前有提供基于NNI自动调参的使用案例么？浏览了几次暂时没看到。

[WenjieDu]

@levisocool 谢谢关注，最近太忙了，没时间弄教程。可以在GitHub上follow我，我们很快会有一篇新论文带着代码一起释出，里面有使用PyPOTS和NNI调参的配置文件供你参考，你到时候可以及时收到提醒。也欢迎加入我们微信社区讨论。