improve: extract method for safe loading yaml file and avoid using PyYaml's FullLoader

[bowenliang123]

Description

• extract a general method for loading YAML file into object, in following step
  • check the file path existence and properly open / close the IO stream in place
  • use yaml's safe_load method
• enable ruff's S506 rule (https://docs.astral.sh/ruff/rules/unsafe-yaml-load/) to avoid possible unsafe yaml loading
• benefits:
  • avoid using yaml.load directly , according to Yaml's docs for deprecation: https://github.com/yaml/pyyaml/wiki/PyYAML-yaml.load(input)-Deprecation
  • skip repeated opening file stream or checking file existence
  • prevent hanging code indent for opening file
  • unified method for handling errors
  • properly covered by unit tests

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?

• add unit tests

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

[bowenliang123]

This PR is ready for review. Please have a check. cc @takatost