Button Auto-Population for External Apps

[ThomasK33]

Enable Coder Desktop to detect and display buttons for external applications automatically. Users desire a seamless, one-click experience for launching native applications such as RDP clients, Zed, Visual Studio Code, and more. This feature will allow Coder Desktop to show relevant buttons based on the configuration of the workspace template.

Initially, we want to display all coder_app's marked with external=true and a set url field that does not have an http or https scheme. (e.g., zed://, rdp://, etc.) as buttons.

This information can be obtained by retrieving the workspace's agent, enumerating all applications, and filtering Coder Desktop-side. When the button is clicked, it should delegate the task of opening the link to the operating system.

To keep the user interface simple and intuitive, we will display a maximum of five buttons, creating a consistent row height. In future iterations, we can explore other options, such as dropdown menus or collapsible sections.