Docs: move submission guidance to GitHub templates (#16232)

* Docs: move submission guidance to GitHub templates

* Docs: make PR risk template entries flexible

* Docs: remove PR reviewer checklist section

docs/docs.json

@@ -1290,7 +1290,7 @@
               },
               {
                 "group": "Contributing",
-                "pages": ["help/submitting-a-pr", "help/submitting-an-issue", "ci"]
+                "pages": ["ci"]
               },
               {
                 "group": "Docs meta",
@@ -1817,10 +1817,6 @@
                 "group": "开发者设置",
                 "pages": ["zh-CN/start/setup"]
               },
-              {
-                "group": "贡献",
-                "pages": ["zh-CN/help/submitting-a-pr", "zh-CN/help/submitting-an-issue"]
-              },
               {
                 "group": "文档元信息",
                 "pages": ["zh-CN/start/hubs", "zh-CN/start/docs-directory"]