syz-cluster: rename the Submit button

Filter is a more appropriate name.

Author: a-nogikh

syz-cluster/dashboard/templates/index.html

@@ -23,7 +23,7 @@
             </label>
           </div>
           <div class="col-auto">
-            <button type="submit" class="btn btn-primary">Submit</button>
+            <button type="submit" class="btn btn-primary">Filter</button>
           </div>
         </div>
       </form>