rebase on Debian 11 "Bullseye" (https://www.debian.org/releases/bullseye/):

- update APT sources lists
- update documentation/download links
- doc: update build process
- increase RAM requirements to 2GB/recommended 4GB
- update tests and build configuration

config/archives/debian-buster-updates-security-backports.list.binary

@@ -1,5 +0,0 @@
-deb https://deb.debian.org/debian/ buster main contrib non-free
-deb http://security.debian.org/ buster/updates main contrib non-free
-deb https://deb.debian.org/debian/ buster-proposed-updates main contrib non-free
-deb https://deb.debian.org/debian/ buster-updates main contrib non-free
-deb https://deb.debian.org/debian/ buster-backports main contrib non-free

config/archives/debian-buster-updates-security-backports.list.chroot

@@ -1 +0,0 @@
-../includes.chroot/etc/apt/sources.list.d/debian-buster-updates-security-backports.list

config/archives/debian-updates-security-backports.list.binary

@@ -0,0 +1,5 @@
+deb https://deb.debian.org/debian/ bullseye main contrib non-free
+deb http://security.debian.org/debian-security bullseye-security main contrib non-free
+deb https://deb.debian.org/debian/ bullseye-proposed-updates main contrib non-free
+deb https://deb.debian.org/debian/ bullseye-updates main contrib non-free
+deb https://deb.debian.org/debian/ bullseye-backports main contrib non-free

config/archives/debian-updates-security-backports.list.chroot

@@ -0,0 +1,5 @@
+deb https://deb.debian.org/debian/ bullseye main contrib non-free
+deb http://security.debian.org/debian-security bullseye-security main contrib non-free
+deb https://deb.debian.org/debian/ bullseye-proposed-updates main contrib non-free
+deb https://deb.debian.org/debian/ bullseye-updates main contrib non-free
+deb https://deb.debian.org/debian/ bullseye-backports main contrib non-free

config/includes.chroot/etc/apt/apt.conf.d/50unattended-upgrades

@@ -20,7 +20,7 @@
 // Within lines unattended-upgrades allows 2 macros whose values are
 // derived from /etc/debian_version:
 //   ${distro_id}            Installed origin.
-//   ${distro_codename}      Installed codename (eg, "buster")
+//   ${distro_codename}      Installed codename (eg, "bullseye")
 Unattended-Upgrade::Origins-Pattern {
         // Codename based matching:
         // This will follow the migration of a release through different