Replace OpenAPI code generation with direct provider schema definitions

[SierraJC]

Currently, we generate provider models and attributes from OpenAPI specs, which creates unnecessary complexity and disconnects between the API and provider designs. This leads to:

1. Multiple schema overrides to fix discrepancies
2. Extra maintenance overhead
3. Less control over the provider schema design

Proposed Solution:

• Remove OpenAPI code generation for provider schemas
• Directly define provider models and attributes in Go
• Keep API client generation for actual API interactions
• Document provider schema separately from API specs
• Keep provider code generation files in source control to help with bootstrapping and detecting API changes?

Benefits:

• Cleaner and more maintainable code
• Better control over provider schema design
• Reduced need for schema overrides