SK-2415 Refactor README for Python SDK v2 (Inspired by Node SDK Improvements)

[skyflow-himanshu]

Why:
We need to clean up and refactor the Python SDK README to improve readability, reduce length and align the structure with Node SDK Readme

Goal:

• Refactor README length under 1000 lines.
• Extracted v2 migration to new /docs directory.
• Extracted advanced initialization options to /docs.
• Extracted advanced bearer token generation.
• Refactor README to increase readability.

[Copilot]

Pull request overview

This PR refactors the Python SDK README by extracting detailed documentation into separate files in a new /docs directory. The changes improve maintainability by separating migration guides, authentication options, and advanced initialization patterns from the main README, reducing its length below 1000 lines while making the documentation more organized and aligned with the Node SDK structure.

Key Changes

• Created comprehensive V1 to V2 migration guide with authentication, initialization, and error handling examples
• Extracted authentication credential options into a dedicated reference document
• Moved advanced multi-vault initialization patterns to a separate guide

Reviewed changes

Copilot reviewed 3 out of 4 changed files in this pull request and generated 7 comments.

File	Description
docs/migrate_to_v2.md	Comprehensive migration guide from V1 to V2 with code examples for authentication, client initialization, request/response structures, and error handling
docs/auth_credentials.md	Reference documentation for all supported authentication credential types with examples
docs/advanced_initialization.md	Guide for advanced client initialization patterns including multi-vault configurations

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