settings: Rename "Automatic" option in color scheme dropdown.

This commit renames "Automatic" option in color scheme setting
dropdown to "Sync with compute". We do not change any variables
used in code just the text in the dropdown visible to user.

Fixes part of #20228.

static/js/settings_config.ts

@@ -48,7 +48,7 @@ export const default_view_values = {
 export const color_scheme_values = {
     automatic: {
         code: 1,
-        description: $t({defaultMessage: "Automatic"}),
+        description: $t({defaultMessage: "Sync with computer"}),
     },
     night: {
         code: 2,

templates/zerver/help/night-mode.md

@@ -13,7 +13,7 @@ for working in a dark space.
 
 {end_tabs}
 
-The default is **Automatic**, which detects which theme to use based
+The default is **Sync with computer**, which detects which theme to use based
 on the color scheme used by your operating system.
 
 You can also specify **Night mode** or **Day mode** if you'd like