Increment engine major version post stabilization (#16743)

Signed-off-by: Alex Peterson <[email protected]>

engine.json

@@ -4,7 +4,7 @@
     "O3DEVersion": "0.1.0.0",
     "O3DEBuildNumber": 0,
     "display_version": "00.00",
-    "version": "2.1.0",
+    "version": "3.0.0",
     "api_versions": {
         "editor": "1.0.0",
         "framework": "1.1.0",