fix: populate app configs to system environment variables

[bowenliang123]

Description

• set the configs read from .env to system env variables, for the packages relies on env variables rather than reading configs from flask app's config.

Type of Change

Please delete options that are not relevant.

• [ ] 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

[laipz8200]

Hello, Bowen! We need to know which packages need to read our configurations from the system environment variables. Could you give us a more specific example?

[bowenliang123]

Hi, @laipz8200 thanks for your attention to this PR, which is raised for :

1. before the removal the config.py in #5507, there's one line to populate all the configs from the .env file to system env vars. see https://github.com/langgenius/dify/pull/5507/files#diff-0e3026d2737181f937735ba5e2023ce7f39a7762c8c2594670f4a944a7e48eafL33

   dotenv.load_dotenv()
   (method comment: "Parse a .env file and then load all the variables found as environment variables...." )

This PR helps to leverage the same efforts to the original behaviours.

2. some users may does use the .env file to set some env vars for the package. eg. setting CO_API_URL as the base URL for cohere package, which is not directly used in Dify.

[laipz8200]

@bowenliang123 Since DifyConfig is read from the .env file, I think we can just use dotenv.load_dotenv() here like we did before.

[bowenliang123]

I would prefer not to reverse couple with the raw dotenv again. For the following reasons,

1. the configs in DifyConfig is ensured for validation in types and range
2. dotenv.load_dotenv method has a implicit file path for .env, if we want to change it in future, it's better to make sure it's aligned with pydantic-settings.
3. Further more pydantic-settings provides various features for arranging the proper order and choices for config sources, like pyproject.toml, JSON files, env files and etc.
4. No benefits or contribution from reusing the dotenv.load_dotenv , it does replicate the configs into system env vars in set_as_environment_variables method by using os.environ[k] = v

[bowenliang123]

Thanks.