[VS Code] Implement a command that triggers selection from available models

Problem to solve

Define a quick way for users to update their user model selections through IDE user/workspace settings.

See also &19346 (comment 2804699353).

Proposal

Trigger a quick pick menu with available models listed as options. If pinned model is present no options should be presented and and be shown a warning message that the group admin has disabled user model selection. Similarly model selection should be disabled for outdated instances or when the feature flag is not available.

Further details

Links / references