pull: Add http2=false remote config option

This seems to work around
https://github.com/ostreedev/ostree/issues/1362

Though I'm not entirely sure why yet. But at least with this it'll be easier for
people to work around things locally.

Closes: #1368
Approved by: jlebon

man/ostree.repo-config.xml

@@ -222,6 +222,14 @@ Boston, MA 02111-1307, USA.
         <listitem><para>Path to file containing trusted anchors instead of the system CA database.</para></listitem>
       </varlistentry>
 
+      <varlistentry>
+        <term><varname>http2</varname></term>
+        <listitem><para>A boolean value, defaults to true.  By
+        default, libostree will use HTTP2; setting this to <literal>false</literal>
+        will disable it.  May be useful to work around broken servers.
+        </para></listitem>
+      </varlistentry>
+
       <varlistentry>
         <term><varname>unconfigured-state</varname></term>
         <listitem><para>If set, pulls from this remote will fail with the configured text.  This is intended for OS vendors which have a subscription process to access content.</para></listitem>