Add deprecation messages

[tom-tan]

It partially fixes #110 by adding deprecation messages for the following features:

• use of label field,
• use of id field with integers, and
• lack of id field.

I also added a tentative deprecation deadline for these features (Currently it is 2023/1/1).
It makes easier for us to decide to remove these features in the future.

Note: it enables to check Deprecate label in the list in #110. We can already check If both label and id are present, then label will be used for messages. in the list.

[codecov]

Codecov Report

Merging #141 (9564970) into main (9672fa5) will increase coverage by 0.34%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #141      +/-   ##
==========================================
+ Coverage   60.04%   60.39%   +0.34%     
==========================================
  Files           2        2              
  Lines         453      457       +4     
  Branches      133      134       +1     
==========================================
+ Hits          272      276       +4     
  Misses        139      139              
  Partials       42       42              

Impacted Files	Coverage Δ
cwltest/__init__.py	64.49% <100.00%> (+0.42%)	⬆️

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[tom-tan]

I added tests to improve coverage!

[mr-c]

Thanks @tom-tan !