Package system: add a notification when a package has been installed

[Giova84]

I noticed that the package system, has already some notifications, eg when there is an error (I noticed this occurs, eg, when a network connection is not available, when I attempt to install local packages). Another scenario is when we install local packages which requires to download dependencies: eg when I installed QBittorrent it takes a while, since it had to download the QT package and some other dependencies, but would be the same from HaikuDepot. Ok: HaikuDepot will show an "active" word in its window, but is not always noticeable (the user can minimize the window, or check for other packages): an average user could be unaware of this, so a notification of "succesfully installed package" would be nice.

Personally I achieve this by using post-install script in my packages: as an example I rely on this:

export sysapps=$(finddir B_SYSTEM_APPS_DIRECTORY)
notify --type important --group "Package Installation" --title "Done" --icon $sysapps/Installer "Wonderful package successfully installed"

which will result as:

[Giova84]

Furthermore wolud be possible use a "progress" notification, for each dependency which is installed.

[leavengood]

Duplicate of #10881. I do not plan to do a progress notification, just a final one.

[nielx]

Remove milestone for tickets with status = closed and resolution != fixed