feat(info): show the install reason and drop the indentation

N? and `info PKG` now print three lines, none indented:

    PKG: <description>
    reason: explicitly installed | installed as a dependency | unknown | not installed
    required by: <installed dependents, comma separated> | nothing

The reason comes from a new <be>_reason backend function: apt-mark
showauto / showmanual (dpkg decides for a package in neither list), the
Install Reason of pacman -Qi, dnf repoquery --installed %{reason} (dnf4
and dnf5 words) and the Installed line of zypper info (rpm plus libzypp's
AutoInstalled when zypper is locked). A row whose old version is "-" is
not installed and the backend is not asked. The "(installed)" qualifier
moves to --help, README and DESIGN.

The rpm E2E fixture and e2e_reset now also mark su-dummy-a and su-dummy-c
as user-installed on dnf, which records plain rpm installs as "unknown",
so 1? and 2? show both reasons on all 12 distros. The verified commands
are recorded in discovery/{apt,pacman,rpm}.md.

tests/unit/data/rpm/db.bash

@@ -51,6 +51,13 @@ declare -A PROVIDES=(
 	[ncurses-libs]=$'ncurses-libs\nlibtinfo.so.6()(64bit)'
 	[redhat-rpm-config]=redhat-rpm-config [rpm]=rpm
 )
+# what dnf4 records as the install reason (`repoquery --installed --qf %{reason}`; the fake dnf
+# speaks dnf5's words with FAKE_DNF_MAJOR=5): plain `rpm -i` leaves "unknown"
+declare -A REASON=(
+	[su-dummy-a]=user [su-dummy-b]=dependency [su-dummy-c]=unknown [su-dummy-d]=user
+	[bash]=user [glibc]=dependency [glibc-common]=dependency [glibc-gconv-extra]=weak-dependency
+	[basesystem]=group [setup]=dependency [filesystem]=dependency
+)
 # FAKE_RPM_NO_D=1: su-dummy-d (which requires every dummy) is not installed
 declare -A FILES=(
 	[su-dummy-a]=/usr/share/su-dummy/su-dummy-a [su-dummy-b]=/usr/share/su-dummy/su-dummy-b