Add getting-started example with external authentication

Author: adutra

LICENSE

@@ -273,6 +273,7 @@ This product includes code from Project Nessie.
 * build-logic/src/main/kotlin/Utilities.kt
 * build-logic/src/main/kotlin/polaris-shadow-jar.gradle.kts
 * build-logic/src/main/kotlin/polaris-runtime.gradle.kts
+* getting-started/assets/keycloak/iceberg-realm.json
 * tools/config-docs/annotations/src/main/java/org/apache/polaris/docs/ConfigDocs.java
 * tools/config-docs/generator/src/main/java/org/apache/polaris/docs/generator/DocGenDoclet.java
 * tools/config-docs/generator/src/main/java/org/apache/polaris/docs/generator/MarkdownFormatter.java

getting-started/README.md

@@ -40,3 +40,6 @@ this directory. Each example has detailed instructions.
   database. The realm is bootstrapped with the Polaris Admin tool. This example also creates a
   `polaris_quickstart` catalog, and offers the ability to run Spark SQL and Trino queries. Finally, it shows how to
   attach a debugger to the Polaris server.
+
+- [Keycloak](keycloak): An example that uses Keycloak as an external identity provider (IDP) for
+  authentication.