feat(ext): Add GNOME Terminal to options

[kgmt0]

Description

This adds a new option for GNOME Terminal in extension preferences. GNOME Terminal is one of the more popular terminal emulators on Linux, so I think it would be nice to have it as an option.

Changes

Checklist

• [x] I have rebased my branch so that it has no conflicts
• [x] I have added tests where appropriate
• [x] Commit messages are compliant with Conventional Commits

Is this a breaking change?

No. This just adds a new option to the extension preferences. Existing options remain unchanged.

Test results

• OS: Linux
• Thunderbird version: 115.2.2

[Frederick888]

Thank you!

I've been a little busy with my personal life recently so there hasn't been much activity in this repo. But I'll try to get back on it asap, hopefully later this month. Thanks in advance for your patience :)

[Frederick888]

Thanks again :)