Add a checkbox to WatermarkController to convert the pdf to pdf-image (#1633)

* Add a checkbox to WatermarkController to convert the pdf to pdf-image

* 381: Fix messages_en_GB

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Co-authored-by: Anthony Stirling <77850077+Frooodle@users.noreply.github.com>

src/main/java/stirling/software/SPDF/model/api/security/AddWatermarkRequest.java

@@ -44,4 +44,7 @@ public class AddWatermarkRequest extends PDFFile {
 
     @Schema(description = "The height spacer between watermark elements", example = "50")
     private int heightSpacer;
+
+    @Schema(description = "Convert the redacted PDF to an image", defaultValue = "false")
+    private boolean convertPDFToImage;
 }