dashboard: Add statIntervalMs field in DegradeRule dialog (#1781)

sentinel-dashboard/src/main/webapp/resources/app/views/dialog/degrade-rule-dialog.html

@@ -68,6 +68,16 @@
 						</div>
 					</div>
 
+					<div class="form-group">
+						<label class="col-sm-2 control-label">统计时长</label>
+						<div class="col-sm-4">
+							<div class="input-group">
+							<input type='number' min="1" class="form-control highlight-border" ng-model='currentRule.statIntervalMs'
+								   placeholder="统计时长(ms)" />
+							<span class="input-group-addon">ms</span>
+							</div>
+						</div>
+					</div>
 
 				</form>
 			</div>