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

**Use case**
People are used to Postgres.
{
    if (pos->type != opening_bracket)
        return false;
    Pos literal_begin = pos;
    Collection arr;
    ParserLiteral literal_p;
    ParserCollectionOfLiterals<Collection> collection_p(opening_bracket, closing_bracket);
    ++pos;
    while (pos.isValid())
    {
        if (!arr.empty())
        {
            if (pos->type == closing_bracket)
            {
                std::shared_ptr<ASTLiteral> literal;