docs: instance generation

[kannann1]

Pull Request

Description

This PR adds comprehensive documentation for Environment Instance Generation, complementing the existing Environment Inventory Generation documentation. The new document explains the instance generation process, includes a detailed Mermaid diagram of the workflow, and clarifies the differences between inventory and instance generation.

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update
• Refactoring (no functional changes)
• Performance improvement
• Test addition or update

Checklist

General

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• I have added tests that prove my fix is effective or that my feature works
• New and existing unit tests pass locally with my changes

Error Handling

• Custom error classes from envgenehelper.errors are used for all error cases
• All error messages include error codes following the ENVGENE-XXXX format
• Error messages are user-friendly and provide clear guidance on how to resolve the issue
• No sensitive information is exposed in error messages
• Errors are propagated to pipeline output and not swallowed by handlers

Error Documentation

• All new error codes are documented in error-catalog.md
• Documentation includes all required sections (ID, Component, When, What, Error, Resolution)
• Error code ranges are used appropriately (business: 0001-1499, validation: 4000-6999, etc.)

Error Testing

• Tests are included for error scenarios
• Error messages are verified to be displayed correctly in the pipeline output

Documentation Changes

• Added new documentation file for Environment Instance Generation
• Documentation follows established format and style guidelines
• Documentation includes clear process flow diagram using Mermaid
• Documentation accurately describes the instance generation process and structure
• Documentation explains outputs between process steps

Related Documentation

• Consistent with existing env-inventory-generation.md documentation
• References to other documentation files are accurate (instance-pipeline-parameters.md)

[github-actions]

All contributors have signed the CLA ✍️ ✅
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[kannann1]

I have read the CLA Document and I hereby sign the CLA