fix: Always inject "page_number" into the config/template context

Author: dannyadair

src/pdfbaker/page.py

@@ -40,6 +40,7 @@ def __init__(
 
             self.page.log_trace_section("Loading page configuration: %s", config_path)
             super().__init__(base_config, config_path)
+            self["page_number"] = page.number
             self.page.log_trace(self.pretty())
 
             self.templates_dir = self["directories"]["templates"]