Implement implicit trigger points for `Create Environment`

[karthiknadig]

[karthiknadig]

Verification Steps:

1. Open a folder containing python file and at least one requirements.txt file.
2. Ensure there are no .venv or .conda in the workspace.
3. The selected python should be the system python (i.e., not a virtual environment)
4. Set python.createEnvironment.trigger to prompt in user settings.
5. Open the python file and click on the run in terminal button at the top right corner in the editor
6. you should see a prompt: