Export to Markdown (#20661)

* Give saveAsExcel its own config options

* Wired up correctly

* Merge conflicts

* PR comments 1

Co-authored-by: Ben Russell <russellben@microsoft.com>

src/sql/platform/query/common/query.ts

@@ -15,6 +15,11 @@ export interface IQueryEditorConfiguration {
 		readonly saveAsExcel: {
 			readonly includeHeaders: boolean,
 		},
+		readonly saveAsMarkdown: {
+			readonly encoding: string,
+			readonly includeHeaders: boolean,
+			readonly lineSeparator: string,
+		}
 		readonly saveAsXml: {
 			readonly formatted: boolean,
 			readonly encoding: string