Adding pagination in list_training_jobs

[Vikas-kum]

Description of changes:

Adding pagination to list_training job api for StopTrainingAction. This action list the training jobs to find a training job which matches the prefix and then takes action on that training job. This PR makes sure that list looks at result for more than one page to find the unique training job. We have put 50 pages as default and we expect that the trainining job would be found in first 50 pages.

Style and formatting:

I have run pre-commit install to ensure that auto-formatting happens with every commit.

Issue number, if available

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[codecov-commenter]

Codecov Report

Merging #323 into master will decrease coverage by 1.42%. The diff coverage is 62.06%.

@@            Coverage Diff             @@
##           master     #323      +/-   ##
==========================================
- Coverage   85.29%   83.86%   -1.43%     
==========================================
  Files          86       86              
  Lines        6352     6367      +15     
==========================================
- Hits         5418     5340      -78     
- Misses        934     1027      +93     

Impacted Files	Coverage Δ
smdebug/rules/action/stop_training_action.py	77.77% <62.06%> (+0.85%)	:arrow_up:
smdebug/tensorflow/keras.py	62.63% <0.00%> (-30.96%)	:arrow_down:
smdebug/core/singleton_utils.py	79.41% <0.00%> (-11.77%)	:arrow_down:
smdebug/tensorflow/base_hook.py	75.19% <0.00%> (-3.82%)	:arrow_down:
smdebug/tensorflow/tensor_ref.py	85.48% <0.00%> (-3.23%)	:arrow_down:
smdebug/tensorflow/utils.py	85.63% <0.00%> (-2.13%)	:arrow_down:
smdebug/tensorflow/collection.py	93.81% <0.00%> (-2.07%)	:arrow_down:
smdebug/core/hook.py	93.02% <0.00%> (-0.22%)	:arrow_down:
smdebug/core/reductions.py	93.47% <0.00%> (ø)
smdebug/core/tensor.py	79.11% <0.00%> (+0.44%)	:arrow_up:
... and 18 more

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