It is not possible to add Python debug configuration

[tolusha]

Description

It is not possible to add Python debug configuration

Reference issue

eclipse-che/che#14219

Reproduction Steps

1. Put Python [1] extension in plugins folder
2. Open any python file to initialize the extension
3. Open launch.json, use completion to select Python
4. Nothing happens

[1] https://marketplace.visualstudio.com/items?itemName=ms-python.python

Diagnostics:
Investigation shows Theia seems to misbehave. Theia collects configurations snippets and shows them during completion in launch.json. But python plugin doesn't have any configurations snippets. The only way to request configurations is to invoke provideDebugConfiguations method when use select Python entry. But it never happens.

How it works in VS Code: