chore: update roadmap content json (#7049)

Co-authored-by: kamranahmedse <4921183+kamranahmedse@users.noreply.github.com>

public/roadmap-content/postgresql-dba.json

@@ -311,6 +311,11 @@
     "title": "MVCC",
     "description": "Multi-Version Concurrency Control (MVCC) is a technique used by PostgreSQL to allow multiple transactions to access the same data concurrently without conflicts or delays. It ensures that each transaction has a consistent snapshot of the database and can operate on its own version of the data.\n\nLearn more from the following resources:",
     "links": [
+      {
+        "title": "Intro to MVCC",
+        "url": "https://www.postgresql.org/docs/current/mvcc-intro.html",
+        "type": "article"
+      },
       {
         "title": "Multiversion concurrency control - Wikipedia",
         "url": "https://en.wikipedia.org/wiki/Multiversion_concurrency_control",
@@ -764,6 +769,11 @@
         "title": "PostgreSQL INTERSECT Operator",
         "url": "https://www.postgresqltutorial.com/postgresql-tutorial/postgresql-intersect/",
         "type": "article"
+      },
+      {
+        "title": "PostgreSQL EXCEPT Operator",
+        "url": "https://www.postgresqltutorial.com/postgresql-tutorial/postgresql-except/",
+        "type": "article"
       }
     ]
   },