Map chart interpolation parameter into sitemap JSON response (openhab#4917)

This was missed in openhab#4610 / commit a9a289e

Signed-off-by: Danny Baumann <dannybaumann@web.de>

Author: maniac103

bundles/org.openhab.core.io.rest.sitemap/src/main/java/org/openhab/core/io/rest/sitemap/internal/SitemapResource.java

@@ -699,6 +699,7 @@ private PageDTO createPageBean(String sitemapName, @Nullable String title, @Null
             bean.legend = chartWidget.getLegend();
             bean.forceAsItem = chartWidget.getForceAsItem();
             bean.yAxisDecimalPattern = chartWidget.getYAxisDecimalPattern();
+            bean.interpolation = chartWidget.getInterpolation();
             if (chartWidget.getRefresh() > 0) {
                 bean.refresh = chartWidget.getRefresh();
             }

bundles/org.openhab.core.io.rest.sitemap/src/main/java/org/openhab/core/io/rest/sitemap/internal/WidgetDTO.java

@@ -68,6 +68,7 @@ public class WidgetDTO {
     public String service;
     public String period;
     public String yAxisDecimalPattern;
+    public String interpolation;
     public Boolean legend;
     public Boolean forceAsItem;
     public Integer row;