feat(editor): add feature flag for code block html preview (#12397)

<!-- This is an auto-generated comment: release notes by coderabbit.ai -->
## Summary by CodeRabbit

- **New Features**
  - Introduced an experimental "Code block HTML preview" feature, allowing users to preview HTML within code blocks when enabled.
- **Settings**
  - Added a toggle in experimental features to enable or disable the code block HTML preview.
- **Localization**
  - Added English translations for the new code block HTML preview feature and its description in workspace settings.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

packages/frontend/core/src/modules/feature-flag/constant.ts

@@ -325,6 +325,15 @@ export const AFFINE_FLAGS = {
     configurable: isBetaBuild || isCanaryBuild,
     defaultState: false,
   },
+  enable_code_block_html_preview: {
+    category: 'affine',
+    displayName:
+      'com.affine.settings.workspace.experimental-features.enable-code-block-html-preview.name',
+    description:
+      'com.affine.settings.workspace.experimental-features.enable-code-block-html-preview.description',
+    configurable: isCanaryBuild,
+    defaultState: true,
+  },
 } satisfies { [key in string]: FlagInfo };
 
 // oxlint-disable-next-line no-redeclare