Integrate CLI recommendation into VS Code extension

[yanzhudd]

Description

This is a draft PR for integrating CLI recommendation into VS Code extension. It just roughly illustrates the code changes of integrating scenario recommendation, and functionality and quality are not yet perfect.

Code changes mainly including the following items:

• Add AzRecommendationProvider class in src.extension.ts file for registering a new completion item provider.
• Add recommend folder in src for adding parse and request logic for CLI recommendation.
• In service.azservice folder, add some logic for CLI recommendation in __main__.py file, including initialize and parse request body from main process.
• In service.azservice folder, add recommend_tooling.py file to request CLI recommendation system to get recommended items.