Kserve Doc for configuring IRSA to access AWS services (#501)

-add documentation for accessing aws service in Kserve with IRSA

#436
kserve/kserve#2003 (comment)
Reference:

https://github.com/kserve/website/blob/main/docs/modelserving/storage/s3/s3.md

website/content/en/docs/component-guides/kserve/access-aws-services-from-kserve.md

@@ -0,0 +1,87 @@
++++
+title = "Configure inferenceService to Access AWS Services from KServe"
+description = "Configuration for accessing AWS services for inference services such as pulling images from private ECR and downloading models from S3 bucket."
+weight = 10
++++
+
+## Access AWS Service from Kserve with IAM Roles for ServiceAccount（IRSA）
+1. Export env values:
+    ```bash
+    export CLUSTER_NAME="<>"
+    export CLUSTER_REGION="<>"
+    export PROFILE_NAMESPACE=kubeflow-user-example-com
+    export SERVICE_ACCOUNT_NAME=aws-sa
+    # 123456789.dkr.ecr.us-west-2.amazonaws.com/kserve/sklearnserver:v0.8.0
+    export ECR_IMAGE_URL="<>"
+    # s3://your-s3-bucket/model
+    export S3_BUCKET_URL="<>"
+    ```
+
+
+1. Create Service Account with IAM Role using [IRSA](https://docs.aws.amazon.com/eks/latest/userguide/iam-roles-for-service-accounts.html). The following command attaches both `AmazonEC2ContainerRegistryReadOnly` and `AmazonS3ReadOnlyAccess` IAM policies:
+    ```
+    eksctl create iamserviceaccount --name ${SERVICE_ACCOUNT_NAME} --namespace ${PROFILE_NAMESPACE} --cluster ${CLUSTER_NAME} --region ${CLUSTER_REGION} --attach-policy-arn=arn:aws:iam::aws:policy/AmazonEC2ContainerRegistryReadOnly --attach-policy-arn=arn:aws:iam::aws:policy/AmazonS3ReadOnlyAccess  --override-existing-serviceaccounts --approve
+    ```
+     > NOTE: You can use ECR (`AmazonEC2ContainerRegistryReadOnly`) and S3 (`AmazonS3ReadOnlyAccess`) ReadOnly managed policies. We recommend creating fine grained policy for production usecase. 
+
+### Deploy models from S3 Bucket 
+1. Create Secret with empty AWS Credential:
+  ```sh
+  cat <<EOF > secret.yaml
+  apiVersion: v1
+      kind: Secret
+      metadata:
+        name: aws-secret
+        namespace: ${PROFILE_NAMESPACE}
+        annotations:
+          serving.kserve.io/s3-endpoint: s3.amazonaws.com
+          serving.kserve.io/s3-usehttps: "1"
+          serving.kserve.io/s3-region: ${CLUSTER_REGION}
+      type: Opaque
+      data:
+        AWS_ACCESS_KEY_ID: ""
+        AWS_SECRET_ACCESS_KEY: ""
+  EOF
+
+  kubectl apply -f secret.yaml
+  ```
+  > NOTE: The **empty** keys for `AWS_ACCESS_KEY_ID/AWS_SECRET_ACCESS_KEY` force it to add the env vars to the init containers but don't override the actual credentials from the IAM role (which happens if you add dummy values). These **empty** keys are needed for IRSA to work in current version and will not be needed in future release.
+
+1. Attach secret to IRSA in your profile namespace:
+    ```
+    kubectl patch serviceaccount ${SERVICE_ACCOUNT_NAME} -n ${PROFILE_NAMESPACE} -p '{"secrets": [{"name": "aws-secret"}]}'
+    ```
+
+
+### Create an InferenceService
+1. Specify the service account in the model server spec :
+> NOTE: make sure you have workable image in `${ECR_IMAGE_URL}`and model in `${S3_BUCKET_URL}` for the inferenceService to work. Versioning of model and image must be consistent: eg. you can not use a v1 model then a v2 image.
+
+  ```sh
+  cat <<EOF > inferenceService.yaml
+  apiVersion: serving.kserve.io/v1beta1
+  kind: InferenceService
+  metadata:
+    name: "sklearn-iris"
+    namespace: ${PROFILE_NAMESPACE}
+    annotations:
+      sidecar.istio.io/inject: "false"
+  spec:
+    predictor:
+      serviceAccountName: ${SERVICE_ACCOUNT_NAME}
+      model:
+        modelFormat:
+          name: sklearn
+        image: ${ECR_IMAGE_URL}
+        storageUri: ${S3_BUCKET_URL}
+  EOF
+
+  kubectl apply -f inferenceService.yaml
+  ```
+    
+1. Check the InferenceService status:
+  ```sh
+  kubectl get inferenceservices sklearn-iris -n ${PROFILE_NAMESPACE}
+  NAME           URL                                                        READY   PREV   LATEST   PREVROLLEDOUTREVISION   LATESTREADYREVISION                    AGE
+  sklearn-iris   http://sklearn-iris.kubeflow-user-example-com.example.com   True           100                              sklearn-iris-predictor-default-00001   105s
+  ```