[AIRFLOW-6884] Make SageMakerTrainingOperator idempotent

[BasPH]

The SageMakerTrainingOperator is currently not idempotent. AWS requires training jobs to have unique names, and training jobs cannot be deleted/updated. Rerunning a SageMakerTrainingOperator will currently raise an exception because it cannot create a training job with the same name.

Therefore I suggest to add an argument action_if_job_exists, which determines the behaviour in case the training job name already exists. Possible options are increment (default) and fail, where increment lists all training jobs prefixed with the given name and suffixes the name with length+1:

Rerunning will result in training job names:
mytrainingjob
mytrainingjob-2
mytrainingjob-3
....

(the training job name is returned - and thus in an XCom, so users can fetch the updated training job name in a successive task)

The fail mode will simply fail if a training job with the same name is encountered.

Additionally, this PR implements a generic method _list_request on the SageMakerHook, for performing list operations on boto3. All boto3 list_* methods follow the same structure and _list_request provides an easy interface to iteratively fetch all results (since AWS returns results in batches).

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Issue link: AIRFLOW-6884

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[codecov-io]

Codecov Report

Merging #7598 into master will decrease coverage by 0.28%.
The diff coverage is 81.63%.

@@            Coverage Diff             @@
##           master    #7598      +/-   ##
==========================================
- Coverage   86.82%   86.53%   -0.29%     
==========================================
  Files         891      896       +5     
  Lines       42095    42740     +645     
==========================================
+ Hits        36549    36986     +437     
- Misses       5546     5754     +208

Impacted Files	Coverage Δ
airflow/providers/amazon/aws/hooks/sagemaker.py	85.96% <76.47%> (-1.29%)	⬇️
...oviders/amazon/aws/operators/sagemaker_training.py	97.29% <93.33%> (-2.71%)	⬇️
airflow/kubernetes/volume_mount.py	44.44% <0%> (-55.56%)	⬇️
airflow/kubernetes/volume.py	52.94% <0%> (-47.06%)	⬇️
airflow/kubernetes/pod_launcher.py	47.18% <0%> (-45.08%)	⬇️
...viders/cncf/kubernetes/operators/kubernetes_pod.py	69.69% <0%> (-25.21%)	⬇️
airflow/kubernetes/refresh_config.py	50.98% <0%> (-23.53%)	⬇️
airflow/utils/helpers.py	71.31% <0%> (-11.19%)	⬇️
airflow/__init__.py	92% <0%> (-8%)	⬇️
airflow/providers/google/cloud/operators/dlp.py	96.25% <0%> (-3.75%)	⬇️
... and 48 more

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