chore: Relocate boto3 to core requirements.txt

[kunwp1]

What changes were proposed in this PR?

This PR moves the boto3 entry from operator-requirements.txt to requirements.txt to reflect its use in the engine core.

Any related issues, documentation, discussions?

Closes #4933

How was this PR tested?

No need to test this PR.

Was this PR authored or co-authored using generative AI tooling?

No.

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 42.16%. Comparing base (056e39d) to head (b27ad9b).

Additional details and impacted files

@@            Coverage Diff            @@
##               main    #4934   +/-   ##
=========================================
  Coverage     42.16%   42.16%           
  Complexity     2180     2180           
=========================================
  Files           980      980           
  Lines         36305    36305           
  Branches       3783     3783           
=========================================
  Hits          15309    15309           
  Misses        20068    20068           
  Partials        928      928           

Flag	Coverage Δ
python	87.38% <ø> (ø)

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