[SPARK-29597][DOCS] Deprecate old Java 8 versions prior to 8u92

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

This PR aims to deprecate old Java 8 versions prior to 8u92.

### Why are the changes needed?

This is a preparation to use JVM Option `ExitOnOutOfMemoryError`.
- https://www.oracle.com/technetwork/java/javase/8u92-relnotes-2949471.html

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

Yes. It's highly recommended for users to use the latest JDK versions of Java 8/11.

### How was this patch tested?

NA (This is a doc change).

Closes #26249 from dongjoon-hyun/SPARK-29597.

Authored-by: Dongjoon Hyun <dhyun@apple.com>
Signed-off-by: Dongjoon Hyun <dhyun@apple.com>

docs/index.md

@@ -47,6 +47,7 @@ locally on one machine --- all you need is to have `java` installed on your syst
 or the `JAVA_HOME` environment variable pointing to a Java installation.
 
 Spark runs on Java 8/11, Scala 2.12, Python 2.7+/3.4+ and R 3.1+.
+Java 8 prior to version 8u92 support is deprecated as of Spark 3.0.0.
 Python 2 support is deprecated as of Spark 3.0.0.
 R prior to version 3.4 support is deprecated as of Spark 3.0.0.
 For the Scala API, Spark {{site.SPARK_VERSION}}