add new alacritty TOML config file

[syphar]

See https://github.com/alacritty/alacritty/releases/tag/v0.13.0 and alacritty/alacritty#6673

All submissions

• I have followed the Contributing Guidelines
• I have checked to ensure there aren't other open Pull Requests for the same update/change

Adding/updating Application X Support

• This PR is only for one application
• It has been added to the list of supported applications in the README
• Changes have been added to the WIP section of the CHANGELOG
• Syncing does not break the application
• Syncing does not compete with any syncing functionality internal to the application
• The configuration syncs the minimal set of data
• No file specific to the local workstation is synced
• No sensitive data is synced

[lra]

Thanks!