Add mongo forward read. Fix markdown code block. (#2174)

* perf: read from mongo forward node

* fix: code block ui

* perf: markdown code css

packages/service/common/mongo/utils.ts

@@ -1,4 +1,6 @@
+import { ReadPreference } from './index';
+
 export const readFromSecondary = {
-  readPreference: 'secondaryPreferred',
-  readConcern: 'local'
+  readPreference: ReadPreference.SECONDARY_PREFERRED, // primary | primaryPreferred | secondary | secondaryPreferred | nearest
+  readConcern: 'local' as any // local | majority | linearizable | available
 };