fix signature logo not loading and add option to disable it (#2143)

* fix signature logo not loading and add option to disable it

* Hardening suggestions for Stirling-PDF / fix-sig-logo (#2144)

Modernize and secure temp file creation

Co-authored-by: pixeebot[bot] <104101892+pixeebot[bot]@users.noreply.github.com>

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Co-authored-by: pixeebot[bot] <104101892+pixeebot[bot]@users.noreply.github.com>

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

@@ -50,4 +50,7 @@ public class SignPDFWithCertRequest extends PDFFile {
             description =
                     "The page number where the signature should be visible. This is required if showSignature is set to true")
     private Integer pageNumber;
+
+    @Schema(description = "Whether to visually show a signature logo along with the signature")
+    private boolean showLogo;
 }