Keyboard Manager - UI for assigning keys is not intuitive

### Description of the new feature / enhancement

I would like to suggest improving the Keyboard Manager UI by adding a dropdown menu in the Action column by default. This would allow users to directly select actions such as Volume Up, Volume Down, Mute, Play/Pause, and other media controls without first needing to press a key to discover the available options.
Currently, the UI appears to encourage users to press the desired key they want to assign. However, this can be confusing when the goal is to create a key that does not physically exist on the keyboard.

### Scenario when this would be used?

A common use case is a bare-bones keyboard that does not include dedicated media keys. In that situation, users may want to remap an unused key to functions such as Volume Up, Volume Down, or Mute.
The current workflow is not very intuitive because it seems to require pressing the key you want to assign, even though that key does not exist on the keyboard. Having a visible dropdown menu with available actions would make the feature much easier to discover and use.

### Supporting information

I use a minimalist keyboard without media controls and wanted to assign some unused keys to media functions. It took me several months to discover that PowerToys can actually assign actions such as Volume Up, Volume Down, and Mute.
The functionality already exists and is very useful, but the current UI makes it difficult to discover. A straightforward dropdown list of available actions would greatly improve usability and help users understand the feature much more quickly.
Thank you for your work on PowerToys and for considering this suggestion.