feat: add endpoint_url parameter to S3SessionManager

[tealgreen0503]

Description

Add endpoint_url parameter to S3SessionManager, enabling use with S3-compatible storage backends (e.g., MinIO, LocalStack) and VPC endpoints. This aligns with the existing BedrockModel pattern.

session_manager = S3SessionManager(
    session_id="my-session",
    bucket="my-bucket",
    endpoint_url="http://localhost:9000",
)

Resolves: #1794

Related Issues

#1794

Documentation PR

N/A

Type of Change

New feature

Testing

• I ran hatch run prepare

Checklist

• I have read the CONTRIBUTING document
• I have added any necessary tests that prove my fix is effective or my feature works
• I have updated the documentation accordingly
• I have added an appropriate example to the documentation to outline the feature, or no new docs are needed
• My changes generate no new warnings
• Any dependent changes have been merged and published

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