Hook up new markdown workspace header suggestion setting (#174004)

Fixes #172977

Also fixes the settingsTree matching settings ids too eagerly

extensions/markdown-language-features/server/src/configuration.ts

@@ -17,6 +17,7 @@ export interface Settings {
 		readonly suggest: {
 			readonly paths: {
 				readonly enabled: boolean;
+				readonly includeWorkspaceHeaderCompletions: 'never' | 'onSingleOrDoubleHash' | 'onDoubleHash';
 			};
 		};