[Enhancement] Allow pausing `.ISO` automatic download.

#### An Example

Currently, it can solely be cancelled:

> ![Screenshot_20240613_170450](https://github.com/FedoraQt/MediaWriter/assets/42837531/de179028-ed76-4ade-a3cb-76ea1433be66)

#### My Environment

I'm using [`5.1.1`](https://github.com/FedoraQt/MediaWriter/releases/tag/5.1.1).