docs: add feature configuration section to Hive federation guide (#2952)

Add documentation for required feature flags when enabling
Hive Metastore federation. Users must configure three properties
in `application.properties` before Hive federation will work:

- `SUPPORTED_CATALOG_CONNECTION_TYPES`
- `SUPPORTED_EXTERNAL_CATALOG_AUTHENTICATION_TYPES`
- `ENABLE_CATALOG_FEDERATION`

Inspired from [this](https://apache-polaris.slack.com/archives/C084XDM50CB/p1761851426511259) Slack thread.

Co-authored-by: Prathyush Shankar <prathyush2018@gmail.com>

Author: carc-prathyush-shankar

site/content/in-dev/unreleased/federation/hive-metastore-federation.md

@@ -40,6 +40,26 @@ property to include `HIVE` (and any other non-REST backends you need):
 `runtime/server/build.gradle.kts` wires the extension in only when this flag is present, so binaries
 built without it will reject Hive federation requests.
 
+## Feature configuration
+
+After building Polaris with Hive support, enable the necessary feature flags in your
+`application.properties` file (or equivalent configuration mechanism such as environment variables or
+a Kubernetes ConfigMap):
+
+```properties
+# Allows both REST and HIVE connection type
+polaris.features."SUPPORTED_CATALOG_CONNECTION_TYPES"=["ICEBERG_REST","HIVE"]
+
+# Allows IMPLICIT authentication, needed for Hive federation
+polaris.features."SUPPORTED_EXTERNAL_CATALOG_AUTHENTICATION_TYPES"=["OAUTH","IMPLICIT"]
+
+# Enables the federation feature itself
+polaris.features."ENABLE_CATALOG_FEDERATION"=true
+```
+
+For Kubernetes deployments, add these properties to the ConfigMap mounted into the Polaris container
+(typically at `/deployment/config/application.properties`).
+
 ## Runtime requirements
 
 - **Metastore connectivity:** Expose the HMS Thrift endpoint (`thrift://host:port`) to the Polaris