### Elasticsearch Version

main @ 1266718e1cdef07a8c7cd1a463707825fabf7277

### Installed Plugins

_No response_

### Java Version

openjdk 17.0.8 2023-07-18

### OS Version

Ubuntu 23.;04

### Problem Description

`DISSECT`'s option `append_separator` is not case insensitive in contrast to all other ESQL keywords.

### Steps to Reproduce

This query works:
```
POST _query?format=txt
{
  "query": """
ROW a = "john jacob jingleheimer schmidt"
| DISSECT a "%{+name} %{+name} %{+name} %{+name}" append_separator="---"
  """
}
```
The identical query with upper cased `APPEND_SEPARATOR` does not:
```
POST _query?format=txt
{
  "query": """
ROW a = "john jacob jingleheimer schmidt"
| DISSECT a "%{+name} %{+name} %{+name} %{+name}" APPEND_SEPARATOR="---"
  """
}
```
It fails with `Invalid option for dissect: [APPEND_SEPARATOR]`.

### Logs (if relevant)

_No response_
x-pack/plugin/esql/src/test/java/org/elasticsearch/xpack/esql/parser/StatementParserTests.java
);
        assertEquals(
            new Row(EMPTY, List.of(new Alias(EMPTY, "c", literalDouble(18446744073709551616.)))),
            statement("row c = 18446744073709551616")
        );
    }
    public void testRowCommandDouble() {
        assertEquals(new Row(EMPTY, List.of(new Alias(EMPTY, "c", literalDouble(1.0)))), statement("row c = 1.0"));
    }
    public void testRowCommandMultivalueInt() {
        assertEquals(new Row(EMPTY, List.of(new Alias(EMPTY, "c", integers(1, 2, -5)))), statement("row c = [1, 2, -5]"));
    }
    public void testRowCommandMultivalueLong() {
        assertEquals(
            new Row(EMPTY, List.of(new Alias(EMPTY, "c", literalLongs(2147483648L, 2147483649L, -434366649L)))),
            statement("row c = [2147483648, 2147483649, -434366649]")
        );
    }
    public void testRowCommandMultivalueLongAndInt() {
        assertEquals(new Row(EMPTY, List.of(new Alias(EMPTY, "c", literalLongs(2147483648L, 1L)))), statement("row c = [2147483648, 1]"));
    }
    public void testRowCommandMultivalueHugeInts() {
        assertEquals(
            new Row(EMPTY, List.of(new Alias(EMPTY, "c", literalDoubles(18446744073709551616., 18446744073709551617.)))),
            statement("row c = [18446744073709551616, 18446744073709551617]")
        );
        assertEquals(
            new Row(EMPTY, List.of(new Alias(EMPTY, "c", literalUnsignedLongs("9223372036854775808", "9223372036854775809")))),
            statement("row c = [9223372036854775808, 9223372036854775809]")
        );