Add plus indicator icons

Author: sirineJ

.changeset/smart-planets-repeat.md

@@ -0,0 +1,5 @@
+---
+"@sumup-oss/icons": minor
+---
+
+Added icons for the Plus tier indicator.

packages/icons/manifest.json

@@ -381,6 +381,21 @@
       "category": "Brand",
       "size": "24"
     },
+    {
+      "name": "plus_tier",
+      "category": "Brand",
+      "size": "16"
+    },
+    {
+      "name": "plus_tier",
+      "category": "Brand",
+      "size": "24"
+    },
+    {
+      "name": "plus_tier",
+      "category": "Brand",
+      "size": "32"
+    },
     {
       "name": "alelo",
       "category": "Card scheme",