Differences in unread message counters for groups (Client/REST-API)

Description:

There seem to be some differences in the counting mechanisms for unread messages between the client and REST-API regarding groups.

Client:
The unread counter for groups does not consider system messages (like when a user is deleted from a group).

REST-API (https://developer.rocket.chat/api/rest-api/methods/groups/counters):
Receiving the number of unread messages for a user and a group via REST-API does consider system messages.

Steps to reproduce:

1. Create a group with three users (A, B, C)
2. Have user A remove user C from the group; Resulting in a system message (User C has been removed...)
3. Write a message with user A in the group
4. Check the unread counters of user B for the group

Expected behavior:

The logic for counting the unread messages should be the same. Either system messages are considered or not.

Actual behavior:

Unread counters of user B in the group:

• In client it shows a 1.
• Receiving the unread counter via REST-API for the user and group returns a 2.

Server Setup Information:

• Version of Rocket.Chat Server: 3.15.0

Start with the groups/counters REST API endpoint and reproduce the three-user group scenario described in the issue. Compare its unread count with the client count after the removal system message and subsequent user message; done means both paths consistently include or exclude system messages.