Add support for foreground controls in PDF generation.

Introduced foreground controls to render elements on top of other content on each page. Updated the Generator and Template classes accordingly, and added unit tests to validate the new functionality.
No version bump is needed because the commit was not yet sent to CI/CD. Due to a workflow issue of mine (forgot i updated the project on github ...) and to keep the history in tact, this was added after the worklow version bump.

README.md

@@ -132,10 +132,13 @@ It has four base sections:
 <template>
     <background>
         <!--
-           All background contents are only rendering the first page.
+           Background is rendered every page and can be used to eg. add fold lines.
+           All background contents are only rendering the first page
+           (to clarify: the available space only accounts for the first page,
+            it is rendered on all pages, but only ever the first page of
+            the contents).
            Background also ignores page margin and padding configuration,
            working with the initial size.
-           Background is rendered every page and can be used to eg. add fold lines.
         -->
     </background>
     <header>
@@ -160,6 +163,17 @@ It has four base sections:
            The footer is repeated and rendered every page, always at the bottom.
         -->
     </footer>
+    <foreground>
+      <!--
+         Foreground is rendered every page and can be used to eg. add fold lines.
+         All foreground contents are only rendering the first page
+         (to clarify: the available space only accounts for the first page,
+          it is rendered on all pages, but only ever the first page of
+          the contents).
+         Foreground also ignores page margin and padding configuration,
+         working with the initial size.
+      -->
+    </foreground>
 </template>
 ```