feat(Keycloak): Support admin bootstrapping for version 26 onwards (#1400)

Author: paulomorgado

src/Testcontainers.Keycloak/KeycloakBuilder.cs

@@ -44,6 +44,7 @@ private KeycloakBuilder(KeycloakConfiguration resourceConfiguration)
     public KeycloakBuilder WithUsername(string username)
     {
         return Merge(DockerResourceConfiguration, new KeycloakConfiguration(username: username))
+            .WithEnvironment("KC_BOOTSTRAP_ADMIN_USERNAME", username)
             .WithEnvironment("KEYCLOAK_ADMIN", username);
     }
 
@@ -55,6 +56,7 @@ public KeycloakBuilder WithUsername(string username)
     public KeycloakBuilder WithPassword(string password)
     {
         return Merge(DockerResourceConfiguration, new KeycloakConfiguration(password: password))
+            .WithEnvironment("KC_BOOTSTRAP_ADMIN_PASSWORD", password)
             .WithEnvironment("KEYCLOAK_ADMIN_PASSWORD", password);
     }
 

tests/Testcontainers.Keycloak.Tests/KeycloakContainerTest.cs

@@ -65,4 +65,13 @@ public KeycloakV25Configuration()
         {
         }
     }
+
+    [UsedImplicitly]
+    public sealed class KeycloakV26Configuration : KeycloakContainerTest
+    {
+        public KeycloakV26Configuration()
+            : base(new KeycloakBuilder().WithImage("quay.io/keycloak/keycloak:26.0").Build())
+        {
+        }
+    }
 }