Add an option to hide image previews

Applies to images, stickers, and URL previews.

Fixes https://github.com/vector-im/riot-web/issues/10735

src/components/views/settings/tabs/user/LabsUserSettingsTab.js

@@ -55,6 +55,7 @@ export default class LabsUserSettingsTab extends React.Component {
                     <SettingsFlag name={"showHiddenEventsInTimeline"} level={SettingLevel.DEVICE} />
                     <SettingsFlag name={"lowBandwidth"} level={SettingLevel.DEVICE} />
                     <SettingsFlag name={"sendReadReceipts"} level={SettingLevel.ACCOUNT} />
+                    <SettingsFlag name={"showImages"} level={SettingLevel.ACCOUNT} />
                 </div>
             </div>
         );