FEATURE: Consolidate link notifications (#26567)

Just like we have for consolidating likes this adds similar
functionality for consolidating links.

spec/requests/api/schemas/json/site_response.json

@@ -74,6 +74,9 @@
         "liked_consolidated": {
           "type": "integer"
         },
+        "linked_consolidated": {
+          "type": "integer"
+        },
         "post_approved": {
           "type": "integer"
         },
@@ -156,6 +159,7 @@
         "watching_first_post",
         "topic_reminder",
         "liked_consolidated",
+        "linked_consolidated",
         "post_approved",
         "code_review_commit_approved",
         "membership_request_accepted",