fix: bucket exists check for session.default_bucket

[mufaddal-rohawala]

Issue #, if available:
#2910
#1990

Description of changes:
Current check for bucket existence in session.py requires s3:ListAllMyBuckets. This permission shouldn't be necessary and is often not allowed in environments following the least privileges principle. Also Without s3:ListAllMyBuckets permissions the case of bucket existence, still requires s3:CreateBucket perms otherwise the check doesn't work properly.

Expected behavior
Users should be able to create a Sagemaker jobs without having to assign s3:ListAllMyBuckets or s3:CreateBucket to the IAM role.

With this change users can now use a s3:ListBucket on a specific bucket, which can support the case of same or cross account specific bucket access.

Testing done:
For backwards compatibility the creation_date check for s3:ListAllMyBuckets would also be supported.
Added units

Merge Checklist

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General

• I have read the CONTRIBUTING doc
• I certify that the changes I am introducing will be backword compatible, and I have discussed concerns about this, if any, with the Python SDK team
• I used the commit message format described in CONTRIBUTING
• I have passed the region in to all S3 and STS clients that I've initialized as part of this change.
• I have updated any necessary documentation, including READMEs and API docs (if appropriate)

Tests

• I have added tests that prove my fix is effective or that my feature works (if appropriate)
• I have added unit and/or integration tests as appropriate to ensure backward compatibility of the changes
• I have checked that my tests are not configured for a specific region or account (if appropriate)
• I have used unique_name_from_base to create resource names in integ tests (if appropriate)

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[sagemaker-bot]

AWS CodeBuild CI Report

• CodeBuild project: sagemaker-python-sdk-unit-tests
• Commit ID: 0bb67c6
• Result: SUCCEEDED
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[codecov-commenter]

Codecov Report

Merging #3165 (0bb67c6) into master (90ede1b) will decrease coverage by 0.00%.
The diff coverage is 87.50%.

@@            Coverage Diff             @@
##           master    #3165      +/-   ##
==========================================
- Coverage   89.63%   89.63%   -0.01%     
==========================================
  Files         200      200              
  Lines       17391    17399       +8     
==========================================
+ Hits        15588    15595       +7     
- Misses       1803     1804       +1     

Impacted Files	Coverage Δ
src/sagemaker/session.py	70.99% <87.50%> (+0.10%)	⬆️

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AWS CodeBuild CI Report

• CodeBuild project: sagemaker-python-sdk-pr
• Commit ID: 0bb67c6
• Result: SUCCEEDED
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• CodeBuild project: sagemaker-python-sdk-local-mode-tests
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• CodeBuild project: sagemaker-python-sdk-notebook-tests
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• CodeBuild project: sagemaker-python-sdk-slow-tests
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AWS CodeBuild CI Report

• CodeBuild project: sagemaker-python-sdk-slow-tests
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[BasilBeirouti]

Thank you @mufaddal-rohawala for writing such a clear description of the problem and for linking the PR issue