MM-22706: pass along set_online flag in websocket response (#14591)

* MM-22706: pass along set_online flag in websocket response

To let the client know whether a user has created a post without
being online or not, we get the set_online query param and
pass it down to the websocket event being passed down to the client.

With this PR, the "data" field of the `posted` event will contain
a `set_online` boolean field set to true/false depending on the
query_param set_online value set in the createPost call.

* Setting to false for auto responder

Co-authored-by: mattermod <mattermod@users.noreply.github.com>

app/channel_test.go

@@ -1142,7 +1142,7 @@ func TestMarkChannelAsUnreadFromPost(t *testing.T) {
 			UserId:    u2.Id,
 			ChannelId: c2.Id,
 			Message:   "@" + u1.Username,
-		}, c2, false)
+		}, c2, false, true)
 		require.Nil(t, err)
 		th.CreatePost(c2)