[SPARK-53513] Update YuniKorn docs with 1.7.0

### What changes were proposed in this pull request?

This PR aims to update `YuniKorn` docs with `1.7.0`.

### Why are the changes needed?

Apache YuniKorn was released on 2025-07-28.
- https://yunikorn.apache.org/release-announce/1.7.0

### Does this PR introduce _any_ user-facing change?

No behavior change.

### How was this patch tested?

Manual review.

### Was this patch authored or co-authored using generative AI tooling?

No.

Closes apache#313 from dongjoon-hyun/SPARK-53513.

Authored-by: Dongjoon Hyun <[email protected]>
Signed-off-by: Dongjoon Hyun <[email protected]>

Author: dongjoon-hyun

README.md

@@ -105,7 +105,7 @@ helm repo add yunikorn https://apache.github.io/yunikorn-release
 
 helm repo update
 
-helm install yunikorn yunikorn/yunikorn --namespace yunikorn --version 1.6.3 --create-namespace --set embedAdmissionController=false
+helm install yunikorn yunikorn/yunikorn --namespace yunikorn --version 1.7.0 --create-namespace --set embedAdmissionController=false
 ```
 
 Submit a Spark app to YuniKorn enabled cluster: