Application buttons - Allow adding & hiding buttons locally

Template authors might add multiple IDEs and editors to cater to a broader group. However, as an individual developer, I might only be interested in VS Code, not JetBrains IDEs. Thus, one can show and hide icons based on personal, locally stored preferences. These can be preferences stored in "global" settings, like the HTTP headers, or on a per workspace level.

The issue names no files, tests, or entry points. Clarify whether preferences are global or workspace-scoped, then identify the existing application-button configuration and define completion around adding, hiding, and persisting buttons locally.

索引モデルが issue の本文から書いたものです。