Add Galaxy workflow generation and validation notebook with example workflow

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I created a notebook that demonstrates how to generate and validate Galaxy workflows. The notebook creates a simple image processing workflow with two steps: Gaussian blur filtering and thresholding. The workflow is saved as a .ga file in JSON format. I initially attempted to use gxformat2 for validation but switched to planemo's test functionality as recommended. The notebook includes code to write the workflow file and attempt validation using planemo, with a helpful message if planemo needs to be installed. This implementation provides a basic template for creating and validating Galaxy workflows programmatically.

• workflow.ga Created a Galaxy workflow file implementing Gaussian blur and threshold operations
• galaxy_workflow_validation.ipynb Created a notebook for generating and validating Galaxy workflows using planemo

closes #123