docs: Use newer Ubuntu LTS in tutorial

docs: Use newer Ubuntu LTS in tutorial

The tutorial uses old 18.04 Bionic Ubuntu release, and tries to
install vpp from packagecloud.io's bionic repository which does not
exist. However newer ubuntu releases' repositories exist, so let's
update to newer Ubuntu LTS version: 22.04 Jammy.

Also, the ubuntu vagrant box is old, so let's replace it to a newer,
generic/ubuntu2204, which uses libvirt provider (instead of virtualbox)
and updated frequently, works well for the tutorial. Due to using
libvirt provider, there is no need to customize the VM as those
customizations are present in the box by default.

The truested=yes part is removed from the apt source list command, as
we add gpgkey anyway, thus, no need for this.

Tutorial and vpp build tested with this new box and looks to be working
fine.

Type: docs
Signed-off-by: Elod Illes <elod.illes@est.tech>
Change-Id: Idcff693240fc6a1496a240e0d07c5ed43fe833e9