`INTERVAL '1 hour'` should be equivalent to `INTERVAL 1 HOUR`

**Use case**
People are used to Postgres.
direction, nulls_direction, nulls_direction_was_explicitly_specified, locale_node,
            has_with_fill, fill_from, fill_to, fill_step);
    node->children.push_back(expr_elem);
    if (locale_node)
        node->children.push_back(locale_node);
    return true;
}
bool ParserFunctionWithKeyValueArguments::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
{
    ParserIdentifier id_parser;
    ParserKeyValuePairsList pairs_list_parser;
    ASTPtr identifier;
    ASTPtr expr_list_args;
    if (!id_parser.parse(pos, identifier, expected))
        return false;
    bool left_bracket_found = false;
    if (pos.get().type != TokenType::OpeningRoundBracket)
    {
        if (!brackets_can_be_omitted)
             return false;
    }
    else
    {
        ++pos;
        left_bracket_found = true;
    }
    if (!pairs_list_parser.parse(pos, expr_list_args, expected))
        return false;
    if (left_bracket_found)
    {