[Feature] Automatically highlight Discord version in installer if only 1 found

### Before Requesting

- [x] I found no existing issue matching my feature request

### Describe the feature you'd like!

When installing (or more usually, reinstalling due to a Discord update), one of the pages of the installer asks you to choose your version, and gives you the choice of Discord, Discord PTB, or Discord Canary. I would like to suggest that when only a single one of those options is found, the installer automatically highlights that option, much in the same way that "Install BetterDiscord" is automatically highlighted on the "Choose an Action" screen.

### Anything else?

_No response_

Start at the installer's Discord version-selection page and compare it with the existing automatic highlight on the "Choose an Action" screen. The work is done when the sole detected option among Discord, Discord PTB, or Discord Canary is highlighted automatically, while multiple detected options still require a choice.

Written by the indexing model from the issue text.