Add bash-completion support for the "apt" command

Add bash-completion support for the "apt" command

The apt bash-completion support was submited to the bash-completion
package as a patch in May 2014. It is still not included to this
date and because it is an important feature for many users it is
now part of apt until the bash-completion package is mantained
more actively again.

Note that the "Relaces" line is only required for Ubuntu it will
have no effect on Debian.

Closes: #747094