Support setting timeout

[b0o]

From notify-send --help:

Usage:
  notify-send [OPTION…] <SUMMARY> [BODY] - create a notification

Help Options:
  -?, --help                        Show help options

Application Options:
  -u, --urgency=LEVEL               Specifies the urgency level (low, normal, critical).
  -t, --expire-time=TIME            Specifies the timeout in milliseconds at which to expire the notification.
  -a, --app-name=APP_NAME           Specifies the app name for the icon
  -i, --icon=ICON[,ICON...]         Specifies an icon filename or stock icon to display.
  -c, --category=TYPE[,TYPE...]     Specifies the notification category.
  -h, --hint=TYPE:NAME:VALUE        Specifies basic extra data to pass. Valid types are int, double, string and byte.
  -v, --version                     Version of the package.

For example:

    return require('desktop-notify').notify("test", vim.log.levels.ERROR, { timeout = 10000 })

Although notify-send calls it expire-time, in my opinion timeout is preferable in order to keep the API compatible with rcarriga/nvim-notify.

As an extension to this suggestion, it would be nice to be able to set the other options accepted by notify-send like icon, category, hint, etc.

[teto]

I concur, for instance I would like to set the icon to a neovim one.