chore: migrate to poetry in devcontainer commands

[perzeuss]

Description

We migrated to poetry but forgot to change it in the devcontainer commands. The commands start-api and start-worker no longer work.

Type of Change

• [ ] 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

Testing Instructions

• [ ] Open the Command Palette with Ctrl+Shift+P.
• [ ] Type and select Dev Containers: Rebuild Container.
• [ ] Wait for the container to rebuild
• [ ] run start-api or start-worker in a terminal, it should now work