updatectl: fix feature JSON parsing (#43617)

## Summary

`updatectl features` failed because it expected the old feature JSON
fields,
while `systemd-sysupdate` now returns `id`, `isEnabled`, and
`documentation`
as an array.

This change:

- Aligns `updatectl` with the current feature JSON schema.
- Unifies JSON output between `systemd-sysupdate`, D-Bus, and Varlink.
- Adds support for multiple `Documentation=` entries for Features and
  Components.
- Exposes and parses `appstream` and `suggested` metadata.
- Propagates condition-evaluation errors through `condition_test_list()`
and
  `feature_is_suggested()`.
- Reports suggestion-evaluation failures instead of silently treating
them as
  `false`.
- Improves JSON dump error handling.
- Expands `TEST-72-SYSUPDATE` coverage and fixes its unknown-field
assertion.
- Documents the `DescribeFeature()` JSON field transition in `NEWS`.
- Keeps the existing Component name list for `sysupdated` compatibility.

The `name`/`enabled` to `id`/`isEnabled` transition is intentional and
documented as a v262 payload change.

Fixes #43603

man/org.freedesktop.sysupdate1.xml

@@ -322,8 +322,8 @@ node /org/freedesktop/sysupdate1/target/host {
 
       <variablelist>
         <varlistentry>
-          <term><literal>name</literal></term>
-          <listitem><para>A string containing the feature's name.</para></listitem>
+          <term><literal>id</literal></term>
+          <listitem><para>A string containing the feature's ID.</para></listitem>
         </varlistentry>
 
         <varlistentry>
@@ -333,18 +333,24 @@ node /org/freedesktop/sysupdate1/target/host {
         </varlistentry>
 
         <varlistentry>
-          <term><literal>enabled</literal></term>
+          <term><literal>isEnabled</literal></term>
           <listitem><para>A boolean indicating whether this feature is enabled.</para></listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><literal>documentationUrl</literal></term>
-          <listitem><para>An optional string that contains a user-presentable HTTP/HTTPS URL to documentation
+          <term><literal>suggested</literal></term>
+          <listitem><para>An optional boolean indicating whether this feature is suggested for enablement. If
+          omitted, it could not be determined whether the feature is suggested.</para></listitem>
+        </varlistentry>
+
+        <varlistentry>
+          <term><literal>documentation</literal></term>
+          <listitem><para>An optional array of strings containing user-presentable HTTP/HTTPS URLs to documentation
           about this feature.</para></listitem>
         </varlistentry>
 
         <varlistentry>
-          <term><literal>appstreamUrl</literal></term>
+          <term><literal>appstream</literal></term>
           <listitem><para>An optional string that contains an HTTP/HTTPS URL to an
           <ulink url="https://wwww.freedesktop.org/software/appstream/docs/chap-CatalogData.html">appstream
           catalog</ulink> XML file containing metadata about this feature.</para></listitem>

man/sysupdate.components.xml

@@ -98,8 +98,9 @@
       <varlistentry>
         <term><varname>Documentation=</varname></term>
 
-        <listitem><para>A user-presentable URL to documentation about this component.
-        This setting supports specifier expansion; see below for details on supported specifiers.</para>
+        <listitem><para>One or more user-presentable URLs to documentation about this component. This setting may be
+        specified more than once. If the empty string is assigned to this option, the list is reset, and all prior
+        assignments have no effect. It supports specifier expansion; see below for details on supported specifiers.</para>
 
         <xi:include href="version-info.xml" xpointer="v262"/></listitem>
       </varlistentry>

man/sysupdate.features.xml

@@ -81,8 +81,11 @@
       <varlistentry>
         <term><varname>Documentation=</varname></term>
 
-        <listitem><para>A user-presentable URL to documentation about this feature.
-        This setting supports specifier expansion; see below for details on supported specifiers.</para>
+        <listitem><para>One or more user-presentable URLs to documentation about this feature. This setting may be
+        specified more than once. If the empty string is assigned to this option, the list is reset, and all prior
+        assignments have no effect. It supports specifier expansion; see below for details on supported specifiers.</para>
+
+        <para>Support for specifying this setting more than once was added in version 262.</para>
 
         <xi:include href="version-info.xml" xpointer="v257"/></listitem>
       </varlistentry>