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

**Use case**
People are used to Postgres.
const char * ParserAdditiveExpression::operators[] =
{
    "+",     "plus",
    "-",     "minus",
    nullptr
};
const char * ParserComparisonExpression::operators[] =
{
    "==",            "equals",
    "!=",            "notEquals",
    "<>",            "notEquals",
    "<=",            "lessOrEquals",
    ">=",            "greaterOrEquals",
    "<",             "less",
    ">",             "greater",
    "=",             "equals",
    "LIKE",          "like",
    "ILIKE",         "ilike",
    "NOT LIKE",      "notLike",
    "NOT ILIKE",     "notILike",
    "IN",            "in",
    "NOT IN",        "notIn",
    "GLOBAL IN",     "globalIn",
    "GLOBAL NOT IN", "globalNotIn",
    nullptr
};
const char * ParserLogicalNotExpression::operators[] =
{
    "NOT", "not",
    nullptr