Add pgAdmin blueprint with Docker Compose and metadata

- Introduced pgAdmin entry in meta.json with relevant details and links.
- Added Docker Compose configuration for pgAdmin service.
- Included pgAdmin logo and template.toml for configuration settings.

meta.json

@@ -1875,5 +1875,22 @@
       "workflow",
       "nextjs"
     ]
+  },
+  {
+    "id": "pgadmin",
+    "name": "pgAdmin",
+    "version": "8.3",
+    "description": "pgAdmin is the most popular and feature rich Open Source administration and development platform for PostgreSQL, the most advanced Open Source database in the world.",
+    "links": {
+      "github": "https://github.com/pgadmin-org/pgadmin4",
+      "website": "https://www.pgadmin.org/",
+      "docs": "https://www.pgadmin.org/docs/"
+    },
+    "logo": "pgadmin.webp",
+    "tags": [
+      "database",
+      "postgres",
+      "admin"
+    ]
   }
 ]