Preserve chart legends in reports (opensearch-project#81) (opensearch…

…-project#84)

Signed-off-by: Joshua Li <joshuali925@gmail.com>
(cherry picked from commit 7b51bd9c433cc28ff3f79d4e5f9a1708a322ef97)

Co-authored-by: Joshua Li <joshuali925@gmail.com>

public/components/visual_report/generate_report.ts

@@ -57,7 +57,7 @@ const removeNonReportElements = (
   reportSource: VISUAL_REPORT_TYPE
 ) => {
   // remove buttons
-  doc.querySelectorAll("[class^='euiButton']").forEach((e) => e.remove());
+  doc.querySelectorAll("button[class^='euiButton']:not(.visLegend__button)").forEach((e) => e.remove());
   // remove top navBar
   doc.querySelectorAll("[class^='euiHeader']").forEach((e) => e.remove());
   // remove visualization editor