feat: add small font size variable

This is needed to create a bit more hyerarchy between more important
and less important text. For example for the talk conversation
description in the header or in NcListItem's "subname"

Signed-off-by: Marco Ambrosini <marcoambrosini@proton.me>

apps/theming/css/default.css

@@ -49,6 +49,7 @@
   --color-border-maxcontrast: #7d7d7d;
   --font-face: system-ui, -apple-system, 'Segoe UI', Roboto, Oxygen-Sans, Cantarell, Ubuntu, 'Helvetica Neue', 'Noto Sans', 'Liberation Sans', Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol', 'Noto Color Emoji';
   --default-font-size: 15px;
+  --font-size-small: 13px;
   /* 1.5 x font-size for accessibility */
   --default-line-height: 1.5;
   --animation-quick: 100ms;

apps/theming/lib/Themes/DefaultTheme.php

@@ -160,6 +160,7 @@ class DefaultTheme implements ITheme {
 
 			'--font-face' => "system-ui, -apple-system, 'Segoe UI', Roboto, Oxygen-Sans, Cantarell, Ubuntu, 'Helvetica Neue', 'Noto Sans', 'Liberation Sans', Arial, sans-serif, 'Apple Color Emoji', 'Segoe UI Emoji', 'Segoe UI Symbol', 'Noto Color Emoji'",
 			'--default-font-size' => '15px',
+			'--font-size-small' => '13px',
 			// 1.5 * font-size for accessibility
 			'--default-line-height' => '1.5',