Added Python sample of obo with frontend and backend structure

[TarunReddy-msft]

Description

Adds a new Python sample under the python/sample directory demonstrating
a frontend-backend structure for Microsoft 365 Copilot agents with OBO Flow.

Included

• README with setup instructions
• Environment variable template
• frontend.py and backend.py files

Testing

• Verified local execution
• No secrets committed

Notes

This change is additive and does not modify existing samples.

[microsoft-github-policy-service]

You are not allowed to delete the mandatory files in this repo.

_{Total execution time: 4.01 seconds}

[TarunReddy-msft]

Closing this PR in favor of a newer PR that includes a cleaner and more complete
implementation of the Python OBO flow sample.

Please refer to the new PR for the updated changes and documentation.
#257