In #193, buster was renamed to bullseye, which caused a regression for
buster: the main "Debian" origin would now be removed. This commit
restores that origin for the default Debian case.

params: debian default: re-add main origin

To ensure people don't trip over old configs, let's validate that the
given origins comply with the current format.

Straight-up removed legacy origins as, after checking, none of the
Debian-based distributions (and thus their derivates) we support still
require legacy-style origin definition.

This is a breaking change.

* Leftover legacy formats in tests removed.
* A typo in the ESM repositories fixed.
* Use correct test specs.

Replace legacy Allowed-Origins with Origins-Pattern on all distros

`legacy_origin` was removed in #204.

README: remove legacy_origin

Add missing 'always' value support to periodic parameters (every n-days)

Add only_on_ac_power option to unattended-upgrades.erb

modulesync 5.3.0

Cleanup legacy fact usage

unattended-upgrades does *not* need special configuration to `dpkg`
for proper operation. It handles those itself. All this does is
changes the `dpkg` configuration for *other* `dpkg` runs.

This will, for example, affect major upgrades, typically done by hand,
and not unattended-upgrades, which was *not* designed for that
purpose. In those cases, unsuspecting users will see their old
configuration file versions silently kept in place, which most
definitely *will* break things on upgrade, rather noisily in the
end.

People unfamiliar with this mechanism will have a hard time figuring
out what has happened, and while recovery is possible, it is tricky
without special tooling. I wrote such a tool here:

https://gitlab.com/anarcat/koumbit-scripts/-/blob/master/vps/clean_conflicts

... but it not well known and definitely not shipped with Debian by
default.

While it is nice that the unattended-upgrades module allows users to
change dpkg options, this can be more easily (and directly) done with
the `apt::conf` parameter in the first place.

This reverts commit 3a4abe4 and
possibly later ones when the options type was introduced.

retire options support

Release 7.0.0