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

**Use case**
People are used to Postgres.
ParserStringLiteral uuid_p;
        ASTPtr ast_uuid;
        if (!uuid_p.parse(pos, ast_uuid, expected))
            return false;
        uuid = parseFromString<UUID>(ast_uuid->as<ASTLiteral>()->value.get<String>());
    }
    if (parts.size() == 1)
        parts.clear();
    node = std::make_shared<ASTIdentifier>(name, std::move(parts));
    node->as<ASTIdentifier>()->uuid = uuid;
    return true;
}
bool ParserFunction::parseImpl(Pos & pos, ASTPtr & node, Expected & expected)
{
    ParserIdentifier id_parser;
    ParserKeyword distinct("DISTINCT");
    ParserExpressionList contents(false);
    ParserSelectWithUnionQuery select;
    bool has_distinct_modifier = false;
    ASTPtr identifier;
    ASTPtr query;
    ASTPtr expr_list_args;
    ASTPtr expr_list_params;
    if (!id_parser.parse(pos, identifier, expected))
        return false;
    if (pos->type != TokenType::OpeningRoundBracket)
        return false;
    ++pos;
    if (distinct.ignore(pos, expected))
        has_distinct_modifier = true;