add concat as alias for array_append scalar

[proddata]

Summary of the changes / Why this improves CrateDB

add concat(array,element) (and array || element) as alias for array_append(array,element) scalar function in line with PostgreSQL

select [1,2,3] || 4 AS array_append;                                                                                                                                                                             
+--------------+
| array_append |
+--------------+
| [1, 2, 3, 4] |
+--------------+

In line with PostgreSQL (see https://www.postgresql.org/docs/15/functions-array.html)

anycompatiblearray || anycompatible → anycompatiblearray
Concatenates an element onto the end of an array (which must be empty or one-dimensional).
ARRAY[4,5,6] || 7 → {4,5,6,7}

Checklist

• Added an entry in CHANGES.txt for user facing changes
• Updated documentation & sql_features table for user facing changes
• Touched code is covered by tests
• CLA is signed
• This does not contain breaking changes, or if it does:
  • It is released within a major release
  • It is recorded in CHANGES.txt
  • It was marked as deprecated in an earlier release if possible
  • You've thought about the consequences and other components are adapted
    (E.g. AdminUI)

[proddata]

Fails here (sometimes) ...

crate/server/src/test/java/io/crate/expression/scalar/ConcatFunctionTest.java

Lines 52 to 53 in e0d75f7

	public void testNormalizeWithNulls() {
	assertNormalize("concat(null, null)", isLiteral(""));

cr> SELECT concat(null,null);                                                                                                                                 
+------+
| NULL |
+------+
| NULL |
+------+
SELECT 1 row in set (0.004 sec)
cr> SELECT concat(null::TEXT,null::TEXT);                                                                                                                     
+----+
| '' |
+----+
|    |
+----+
SELECT 1 row in set (0.011 sec)

and here ...

crate/server/src/test/java/io/crate/expression/scalar/ConcatFunctionTest.java

Lines 87 to 88 in e0d75f7

	public void testArrayWithAUndefinedInnerType() throws Exception {
	assertNormalize("concat([], [1, 2])", isLiteral(List.of(1, 2)));

SELECT concat([], [1, 2]);                                                                                                                                
-- UnsupportedFeatureException[Unknown function: concat([], _array(1, 2)), no overload found for matching argument types: (undefined_array, integer_array). Possible candidates: concat(text, text):text, concat(text):text, concat(array(E), array(E)):array(E), concat(array(E), E):array(E), concat(object, object):object]

---

I would assume, in both cases it is a problem with precedence? ideas?