Update Operator compatibility matrix and honor functional tests compa…

…tibility (#792)

### Description
Update Operator compatibility matrix and honor compatibility for
functional tests

### Issues Resolved
Coming from
#776 (comment).
This should also fix
#760.

### Check List
- [x] Commits are signed per the DCO using --signoff 
- [x] Unittest added for the new/changed functionality and all unit
tests are successful
- [ ] Customer-visible features documented
- [ ] No linter warnings (`make lint`)

If CRDs are changed:
- [ ] CRD YAMLs updated (`make manifests`) and also copied into the helm
chart
- [ ] Changes to CRDs documented

Please refer to the [PR
guidelines](https://github.com/opensearch-project/opensearch-k8s-operator/blob/main/docs/developing.md#submitting-a-pr)
before submitting this pull request.

By submitting this pull request, I confirm that my contribution is made
under the terms of the Apache 2.0 license.
For more information on following Developer Certificate of Origin and
signing off your commits, please check
[here](https://github.com/opensearch-project/OpenSearch/blob/main/CONTRIBUTING.md#developer-certificate-of-origin).

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

.github/workflows/functional-tests.yaml

@@ -44,6 +44,12 @@ jobs:
 
   cluster-helm-chart:
     runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        version:
+            - 2.13.0
+            - 1.3.16
     steps:
       - name: Checkout code
         uses: actions/checkout@v4
@@ -77,7 +83,7 @@ jobs:
 
           ## Install helm chart
           helm install opensearch-operator ../charts/opensearch-operator --set manager.image.repository=controller --set manager.image.tag=latest --set manager.image.pullPolicy=IfNotPresent --namespace default --wait
-          helm install opensearch-cluster ../charts/opensearch-cluster --set OpenSearchClusterSpec.enabled=true --wait
+          helm install opensearch-cluster ../charts/opensearch-cluster --set  opensearchCluster.general.version=${{ matrix.version }} --set opensearchCluster.dashboards.version=${{ matrix.version }} --wait
           cd functionaltests
 
           ## Run tests

README.md

@@ -49,14 +49,11 @@ The Operator can be easily installed using Helm:
 
 The opensearch k8s operator aims to be compatible to all supported opensearch versions. Please check the table below for details:
 
-| Operator Version | Min Supported Opensearch Version | Max supported Opensearch version | Comment |
-|------------------|----------------------------------|----------------------------------|---------|
-| 2.3              | 1.0                              | 2.8                              |         |
-| 2.2              | 1.0                              | 2.5                              |         |
-| 2.1              | 1.0                              | 2.3                              |         |
-| 2.0              | 1.0                              | 2.3                              |         |
-| 1.x              | 1.0                              | 1.x                              |         |
-| 0.x              | 1.0                              | 1.x                              | Beta    |
+
+| Operator Version                                            | Min Supported Opensearch Version | Max Supported Opensearch Version | Comment                                     |
+| ----------------------------------------------------------- | -------------------------------- | -------------------------------- | ------------------------------------------- |
+| 2.6.0<br>2.5.1<br>2.5.0 | 1.3.x                            | latest 2.x                       | Supports the latest OpenSearch 2.x version. |
+
 
 This table only lists versions that have been explicitly tested with the operator, the operator will not prevent you from using other versions. Newer minor versions (2.x) not listed here generally also work but you should proceed with caution and test it our in a non-production environment first.