chore(editor): add edgeless scribbled style feature flag (#11127)

Closes: [BS-2805](https://linear.app/affine-design/issue/BS-2805/下掉线条样式切换功能，需添加-feature-flag)

blocksuite/affine/shared/src/services/feature-flag-service.ts

@@ -19,6 +19,7 @@ export interface BlockSuiteFlags {
   enable_block_meta: boolean;
   enable_callout: boolean;
   enable_embed_iframe_block: boolean;
+  enable_edgeless_scribbled_style: boolean;
 }
 
 export class FeatureFlagService extends StoreExtension {
@@ -42,6 +43,7 @@ export class FeatureFlagService extends StoreExtension {
     enable_block_meta: false,
     enable_callout: false,
     enable_embed_iframe_block: false,
+    enable_edgeless_scribbled_style: false,
   });
 
   setFlag(key: keyof BlockSuiteFlags, value: boolean) {