Add UNSTRUCTURED_API_KEY env support

[majian159]

Description

Please include a summary of the change and which issue is fixed. Please also include relevant motivation and context. List any dependencies that are required for this change.

Fixes # (issue)

Type of Change

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• 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)
• This change requires a documentation update, included: Dify Document
• Improvement, including but not limited to code refactoring, performance optimization, and UI/UX improvement
• Dependency upgrade

How Has This Been Tested?

Please describe the tests that you ran to verify your changes. Provide instructions so we can reproduce. Please also list any relevant details for your test configuration

• TODO

Suggested Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• My changes generate no new warnings
• I ran dev/reformat(backend) and cd web && npx lint-staged(frontend) to appease the lint gods
• optional I have made corresponding changes to the documentation
• optional I have added tests that prove my fix is effective or that my feature works
• optional New and existing unit tests pass locally with my changes

[JohnJyong]

UNSTRUCTURED_API_KEY is not a necessary variable ， pls add the default value for it in the file config.py , thanks
@majian159

[crazywoola]

See comments

[majian159]

UNSTRUCTURED_API_KEY is not a necessary variable ， pls add the default value for it in the file config.py , thanks @majian159

Specifically, how should it be done? UNSTRUCTURED_API_KEY is similar in nature to UNSTRUCTURED_API_URL. I noticed that UNSTRUCTURED_API_KEY does not have any other default configuration in config.py.

[JohnJyong]

After test, api_key works fine with None value , approved

After test, api_key works fine with None value