Python: Remove duplicated workflow observability sample

[TaoChenOSU]

Motivation and Context

Closes #2184

Description

1. Remove the workflow observability sample folder under getting_started/workflows ad point to the one under getting_started/observability

Documentation will be updated in the docs repo.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the Contribution Guidelines
• All unit tests pass, and I have added new tests where possible
• Is this a breaking change? If yes, add "[BREAKING]" prefix to the title of the PR.

[Copilot]

Pull Request Overview

This PR consolidates duplicate observability samples by removing the workflow-specific observability sample and directing users to the centralized observability examples directory.

• Removes python/samples/getting_started/workflows/observability/tracing_basics.py
• Updates workflows README to reference the main observability samples directory
• Enhances documentation in workflow_observability.py with detailed workflow description and telemetry span information

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
python/samples/getting_started/workflows/observability/tracing_basics.py	Deleted duplicate observability sample previously located in workflows directory
python/samples/getting_started/workflows/README.md	Updated observability section to redirect users to the main observability samples directory with proper links
python/samples/getting_started/observability/workflow_observability.py	Enhanced documentation with detailed workflow description, telemetry span categories, and prerequisites