feat(coderd): add inbox notifications endpoints (#16889)

This PR is part of the inbox notifications topic, and rely on previous
PRs merged - it adds :

- Endpoints to : 
  - WS : watch new inbox notifications
  - REST : list inbox notifications
  - REST : update the read status of a notification

Also, this PR acts as a follow-up PR from previous work and : 

- fix DB query issues
- fix DBMem logic to match DB

coderd/notifications/dispatch/inbox_test.go

@@ -73,7 +73,7 @@ func TestInbox(t *testing.T) {
 		t.Run(tc.name, func(t *testing.T) {
 			t.Parallel()
 
-			db, _ := dbtestutil.NewDB(t)
+			db, pubsub := dbtestutil.NewDB(t)
 
 			if tc.payload.UserID == "valid" {
 				user := dbgen.User(t, db, database.User{})
@@ -82,7 +82,7 @@ func TestInbox(t *testing.T) {
 
 			ctx := context.Background()
 
-			handler := dispatch.NewInboxHandler(logger.Named("smtp"), db)
+			handler := dispatch.NewInboxHandler(logger.Named("smtp"), db, pubsub)
 			dispatcherFunc, err := handler.Dispatcher(tc.payload, "", "", nil)
 			require.NoError(t, err)