> (you don't have to strictly follow this form)

**Use case**

Sometimes, for really sophisticated scenarios it can be hard to control the amount of in-progress backups run externally. For the purpose of simpler control we can introduce server-level setting which disallows running concurrent backups of any type. 

Something like this in `config.xml` (enabled by default):
`<allow_concurrent_backups>true</allow_concurrent_backups>`

**Describe the solution you'd like**

It's important that backups can be executed in distributed way on multiple servers. Need to take it into account.

**Describe alternatives you've considered**
External check of `system.backups` table, but it can be complex.

{
            table_function_ptr = TableFunctionFactory::instance().get(table_expression, shared_from_this());
        }
        catch (Exception & e)
        {
            if (e.code() == ErrorCodes::UNKNOWN_FUNCTION)
            {
                e.addMessage(" or incorrect parameterized view");
            }
            throw;
        }
        if (getSettingsRef().use_structure_from_insertion_table_in_table_functions && table_function_ptr->needStructureHint() && hasInsertionTable())
        {
            const auto & structure_hint = DatabaseCatalog::instance().getTable(getInsertionTable(), shared_from_this())->getInMemoryMetadataPtr()->getColumns();
            bool use_columns_from_insert_query = true;
            
            if (select_query_hint && getSettingsRef().use_structure_from_insertion_table_in_table_functions == 2)
            {
                const auto * expression_list = select_query_hint->select()->as<ASTExpressionList>();
                std::unordered_set<String> virtual_column_names = table_function_ptr->getVirtualsToCheckBeforeUsingStructureHint();
                Names columns_names;
                bool have_asterisk = false;
                
                
                for (const auto & expression : expression_list->children)
                {
                    if (auto * identifier = expression->as<ASTIdentifier>())
                    {
                        columns_names.push_back(identifier->name());
                    }