[Feat]: Implement Workspace Selection Dropdown for '@' Command

[yatendra2001]

Is your feature request related to a problem?

Users need an intuitive way to include their entire workspace as context when typing queries in the chat interface.

Describe the solution that you'd like

Introduce a feature where typing '@' in the chat input triggers a dropdown menu with the option to select the workspace. This will signal the extension to include the entire workspace as context for the subsequent query.

Describe alternatives that you have considered

No response

Additional Information

@workspace must be a part of string input.

Refer this image of co-pilot:

Acceptance Criteria

1. Typing '@' in the chat input shows a dropdown with the workspace selection.
2. Selecting the workspace from the dropdown appends a special tag to the chat input.
3. The UI for the dropdown is consistent with the chat interface and VSCode's design language.

[wadhia-yash]

Hi @yatendra2001 I would like to take up the task

[yatendra2001]

assigned @wadhia-yash

[yatendra2001]

closed by pr #164