[Release 2.9.0] Add k-NN back (#3734)

Signed-off-by: Prudhvi Godithi <[email protected]>

manifests/2.9.0/opensearch-2.9.0.yml

@@ -32,15 +32,15 @@ components:
     checks:
       - gradle:properties:version
       - gradle:dependencies:opensearch.version
-#  - name: k-NN
-#    repository: https://github.com/opensearch-project/k-NN.git
-#    ref: '2.9'
-#    platforms:
-#      - linux
-#      - windows
-#    checks:
-#      - gradle:properties:version
-#      - gradle:dependencies:opensearch.version
+  - name: k-NN
+    repository: https://github.com/opensearch-project/k-NN.git
+    ref: '2.9'
+    platforms:
+      - linux
+      - windows
+    checks:
+      - gradle:properties:version
+      - gradle:dependencies:opensearch.version
   - name: geospatial
     repository: https://github.com/opensearch-project/geospatial.git
     ref: '2.9'