A better way to show Borg's errors

[ahmedhosssam]

Description

Fixes #1940

I think it would be better to show Borg's error messages inside Vorta's exception dialog instead of relying on the tiny progress event box.
Now most of Borgs' commands would have a "started" and "finished" messages appears in the progress event box, and the errors would appear in the exception dialog.

I also added finished_event function to mount and umuont, I'm not sure but I think it should have error handling also, just as the rest of the commands.

Now the command that doesn't have that change are info_archive, info_repo, init, version, and rename.

Related Issue

#1940

How Has This Been Tested?

I tested it by changing Borg's commands from the source code to force them to fail and return non-zero code, and the result for all the commands is just like the screen record.

Screen Record:

2025-03-20.03-14-30.mp4

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• I have read the CONTRIBUTING guide.
• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing tests passed.

I provide my contribution under the terms of the license of this repository and I affirm the Developer Certificate of Origin.