test: add step to set mock response with explicit header

Add 'set the response with :header header :value to:' step to the
test FeatureContext so scenarios can control the Content-Type (or any
other header) of the mock server response, making header assertion
scenarios deterministic.

Signed-off-by: Vitor Mattos <1079143+vitormattos@users.noreply.github.com>

Author: vitormattos

features/bootstrap/FeatureContext.php

@@ -139,6 +139,14 @@ public function setTheResponseTo(PyStringNode $response): void {
 		));
 	}
 
+	#[Given('set the response with :header header :value to:')]
+	public function setTheResponseWithHeaderTo(string $header, string $value, PyStringNode $response): void {
+		$this->mockServer->setDefaultResponse(new MockWebServerResponse(
+			(string) $response,
+			[$header => $value]
+		));
+	}
+
 	/**
 	 * @inheritDoc
 	 */