[Fix] Minor fix for AMLC Tutorial - QA

[sxjscience]

Description

Some documentation improvement + Use dataclass

Checklist

Essentials

• [ ] PR's title starts with a category (e.g. [BUGFIX], [MODEL], [TUTORIAL], [FEATURE], [DOC], etc)
• [ ] Changes are complete (i.e. I finished coding on this PR)
• [ ] All changes have test coverage
• [ ] Code is well-documented

Changes

• [ ] Feature1, tests, (and when applicable, API doc)
• [ ] Feature2, tests, (and when applicable, API doc)

Comments

• If this change is a backward incompatible change, why must this change be made.
• Interesting edge cases to note here

cc @dmlc/gluon-nlp-team

[codecov[bot]]

Codecov Report

Merging #1359 into master will increase coverage by 10.84%. The diff coverage is 50.00%.

@@             Coverage Diff             @@
##           master    #1359       +/-   ##
===========================================
+ Coverage   70.87%   81.71%   +10.84%     
===========================================
  Files         105       52       -53     
  Lines       12483     6898     -5585     
===========================================
- Hits         8847     5637     -3210     
+ Misses       3636     1261     -2375     

Impacted Files	Coverage Δ
setup.py	0.00% <ø> (ø)
src/gluonnlp/utils/preprocessing.py	94.28% <50.00%> (-5.72%)	:arrow_down:
src/gluonnlp/models/xlmr.py	58.82% <0.00%> (-29.42%)	:arrow_down:
src/gluonnlp/models/__init__.py	67.74% <0.00%> (-29.04%)	:arrow_down:
src/gluonnlp/models/electra.py	57.89% <0.00%> (-18.56%)	:arrow_down:
src/gluonnlp/models/bart.py	70.62% <0.00%> (-15.63%)	:arrow_down:
src/gluonnlp/utils/config.py	61.53% <0.00%> (-15.39%)	:arrow_down:
src/gluonnlp/models/roberta.py	84.38% <0.00%> (-9.29%)	:arrow_down:
src/gluonnlp/utils/misc.py	51.08% <0.00%> (-7.74%)	:arrow_down:
src/gluonnlp/models/albert.py	87.80% <0.00%> (-7.67%)	:arrow_down:
... and 61 more

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