refactor: Rename appearance to theme (#3237)

* refactor: Rename appearance to theme

* fix

* update changelog

* rename theme_dark to theme--dark

* add about migration

src/appState.ts

@@ -13,7 +13,7 @@ export const getDefaultAppState = (): Omit<
   "offsetTop" | "offsetLeft"
 > => {
   return {
-    appearance: "light",
+    theme: "light",
     collaborators: new Map(),
     currentChartType: "bar",
     currentItemBackgroundColor: "transparent",
@@ -92,7 +92,7 @@ const APP_STATE_STORAGE_CONF = (<
 >(
   config: { [K in keyof T]: K extends keyof AppState ? T[K] : never },
 ) => config)({
-  appearance: { browser: true, export: false },
+  theme: { browser: true, export: false },
   collaborators: { browser: false, export: false },
   currentChartType: { browser: true, export: false },
   currentItemBackgroundColor: { browser: true, export: false },