chore: migrate cos-sdk examples from ibm-cos-sdk v1 to v2

[veronika-alraheem]

Checklist

• Added tests for code changes or test/build only changes
• Updated the change log file (CHANGES.md) or test/build only changes
• Completed the PR template below:

Description

Updated the cos examples to use the v2 ibm-cos-sdk
Fixes i592

Approach

• Migrate IBM COS SDK usage from v1 to v2
• Update object operations to use S3Client and command patterns
• Convert API calls from chained method calls to the command pattern
• Added --cos_region option to all scripts
• Replaced ~/.bluemix/cos_credentials file with IBM_API_KEY_ID and IBM_SERVICE_INSTANCE_ID environment variables for COS authentication
• Updated README.md

Schema & API Changes

• "No change"

Security and Privacy

• "No change"

Testing

• N/A build or packaging only changes

Monitoring and Logging

• "No change"