Show Enable Code Suggestions popup as part of user onboarding flow

Belongs to epic &12106 (closed) which comprises of:

• #1115 (closed)
• #1116
• #1117

As part of #1116 there exists a popup to allow the user to enable Code Suggestions at the GitLab instance settings.

This issue is to show that popup at the "right" moment during onboarding.

1. User must be authenticated in the GitLab extension
2. User must have added an account
3. GitLab instance API must support Code Suggestions
4. Show popup