Update warnings in TrainingTricksConnector

[rohitgr7]

What does this PR do?

Improved some warnings and checks since there is some ambiguity.

>>> GradClipAlgorithmType.NORM == 'Norm'  # weird
True

>>> 'Norm' in list(GradClipAlgorithmType)  # weird
True

>>> GradClipAlgorithmType('Norm')   # okay
ValueError: 'Norm' is not a valid GradClipAlgorithmType

>>> Trainer(gradient_clip_algorithm = 'Norm')  # not a good warning
ValueError: 'Norm' is not a valid GradClipAlgorithmType
    
>>> Trainer(gradient_clip_algorithm = 'something_else')   # not user-friendly
gradient_clip_algorithm should be in [<GradClipAlgorithmType.VALUE: 'value'>, <GradClipAlgorithmType.NORM: 'norm'>]

Now both 'Norm' and 'norm' are valid

Does your PR introduce any breaking changes? If yes, please list them.

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[github-actions]

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[codecov]

Codecov Report

Merging #9595 (605c07f) into master (c66d30a) will increase coverage by 1%.
The diff coverage is 100%.

@@           Coverage Diff           @@
##           master   #9595    +/-   ##
=======================================
+ Coverage      92%     93%    +1%     
=======================================
  Files         181     179     -2     
  Lines       15728   15317   -411     
=======================================
- Hits        14446   14209   -237     
+ Misses       1282    1108   -174