Add an option (button) to mount & open the AppImage in the appimage launch UI

[iTrooz]

Pre-submit checks

• [X] I checked for similar issues beforehand, but could not find any. I could not add my proposal to any existing issue.
• [X] I am going to take the time to to fill in all the required details. I know that the bug report will be dismissed otherwise.

Feature description

I would like appimage-launcher to give an option to mount and open the appimage in the file explorer

Proposed solution

A button on appimage-launcher's UI to do that, for example in the bottom left

Alternative solutions you considered

No response

Additional context

I'm willing to submit a PR to add this feature to appimage-launcher

[iTrooz]

Message sent by TheAssassin in #appimage :

TheAssassin/AppImageLauncher#515 is not going to end up in 3.0

(I'm just documenting things said)