Check max users on user creation

Summary

• fix: check max users on user creation

• test: role and user limits

Due to the fact that we don't use two stage commit for ACL, we have to check all the ACL preconditions both in SQL preprocessing (as a short circuit) and in CAS (for consistency), also CAS can be called directly

---

• Close #1208 (closed)
• Cherry-pick to: none
• Docs follow-up: not necessary
• Changelog is updated

test/int/test_limits.py

+import pytest
+from conftest import Cluster, TarantoolError
+
+max_picodata_users = 26
+
+def test_user_limit(cluster: Cluster):
+    cluster.deploy(instance_count=2)
+    i1, i2 = cluster.instances
+
+    password = "Passw0rd"
+
+    for i in range(max_picodata_users):
+        username = f"USER{i}"
+
+        acl = i1.sql(
+            f"""
+            create user {username} with password '{password}'
+            using md5 option (timeout = 3)
+            """
+        )
+        assert acl["row_count"] == 1
+
+    # FIXME: should not panic, should be an error instead
+    with pytest.raises(
+        TarantoolError,
+        match="a limit on the total number of users has been reached: 32",
+    ):
+        username = f"USER{max_picodata_users}"
+        i1.sql(
+            f"""
+            create user {username} with password '{password}'
+            using md5
+            """
+        )
+
+def test_role_limit(cluster: Cluster):
+    cluster.deploy(instance_count=2)
+    i1, i2 = cluster.instances
+
+    for i in range(max_picodata_users):
+        role = f"ROLE{i}"
+
+        acl = i1.sql(f"create role {role}")
+        assert acl["row_count"] == 1
+
+    # FIXME: should not panic, should be an error instead
+    with pytest.raises(
+        TarantoolError,
+        match="a limit on the total number of users has been reached: 32",
+    ):
+        role = f"ROLE{max_picodata_users}"
+        i1.sql(f"create role {role}")