[scorecards] allow different default plan and methodology years

There are points when we want to display the next year's scorecards
methodology as the default rather than the cuurent years to add a
METHODLOGY_YEAR setting and use that in place of the PLAN_YEAR if we're
not viewing a specific year.

proj/settings.py

@@ -154,6 +154,7 @@
 RELATED_SEARCH_THRESHOLD_LOOSE = 0.5
 
 PLAN_YEAR = 2023
+METHODOLOGY_YEAR = 2025
 
 PLAN_SCORECARD_DATASET_DETAILS = {
     "org": "mysociety",

scoring/templates/scoring/methodology.html

@@ -5,7 +5,7 @@
     <div class="methodology-2023-content js-dynamic-content ">
         <div class="pt-5 pb-6 pt-lg-8 pb-lg-8 hero-section with-version-background">
             <div class="d-flex flex-column align-items-end align-items-lg-start hero-version-badge position-absolute">
-                <span class="version-year d-block fw-bold lh-1">2023</span>
+                <span class="version-year d-block fw-bold lh-1">{{ methodology_year }}</span>
                 <span class="version-name d-block fw-bold lh-1">Action Scorecards</span>
             </div>
             <div class="container">

scoring/views.py

@@ -914,15 +914,20 @@ def get_context_data(self, **kwargs):
         context["page_title"] = "Methodology"
         context["current_page"] = "methodology-page"
 
+        methodology_year = self.request.year
+        if kwargs.get("year") is None:
+            methodology_year = settings.METHODOLOGY_YEAR
+
+        context["methodology_year"] = methodology_year
         context[
             "intro_template"
-        ] = f"scoring/methodology/{self.request.year}/_intro.html"
+        ] = f"scoring/methodology/{methodology_year}/_intro.html"
         context[
             "details_template"
-        ] = f"scoring/methodology/{self.request.year}/_details.html"
+        ] = f"scoring/methodology/{methodology_year}/_details.html"
 
         questions = (
-            PlanQuestion.objects.filter(section__year=self.request.year)
+            PlanQuestion.objects.filter(section__year=methodology_year)
             .select_related("section")
             .order_by("section__code", "code")
         )