Fix setuptools deprecation warnings in setup.py

[adev-code]

When building botocore with python -m build -w, setuptools generates deprecation warnings:

1. License classifier warning: The License :: OSI Approved :: Apache Software License classifier is deprecated in favor of SPDX license expressions
2. Package discovery warnings: botocore.data directories are not included in the packages configuration, causing setuptools to warn they may be ignored

This PR fixes setuptools deprecation warnings that appear during package building as described above.

Changes Made

• Removed deprecated License :: OSI Approved :: Apache Software License from classifiers
• Added license="Apache-2.0" field using SPDX identifier
• Replaced find_packages() with find_namespace_packages() to properly include data-only directories
• Updated import to include find_namespace_packages

Testing

• Verified python -m build -w runs without warnings
• Confirmed package installation still works correctly
• All existing functionality preserved

Resolves: #3434

[codecov-commenter]

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Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.19%. Comparing base (bbed2c0) to head (f423e6c).
⚠️ Report is 219 commits behind head on develop.
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Additional details and impacted files

@@             Coverage Diff             @@
##           develop    #3565      +/-   ##
===========================================
+ Coverage    93.13%   93.19%   +0.05%     
===========================================
  Files           68       68              
  Lines        15336    15411      +75     
===========================================
+ Hits         14283    14362      +79     
+ Misses        1053     1049       -4     

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