[ESQL] Add SPACE function (#112350)

Adds the SPACE(number) function, which is equivalent to REPEAT(" ", number).

Author: chrisberkhout

docs/changelog/112350.yaml

@@ -0,0 +1,5 @@
+pr: 112350
+summary: "[ESQL] Add `SPACE` function"
+area: ES|QL
+type: enhancement
+issues: []

docs/reference/esql/functions/description/space.asciidoc

@@ -19,6 +19,7 @@
 * <<esql-replace>>
 * <<esql-right>>
 * <<esql-rtrim>>
+* <<esql-space>>
 * <<esql-split>>
 * <<esql-starts_with>>
 * <<esql-substring>>
@@ -39,6 +40,7 @@ include::layout/repeat.asciidoc[]
 include::layout/replace.asciidoc[]
 include::layout/right.asciidoc[]
 include::layout/rtrim.asciidoc[]
+include::layout/space.asciidoc[]
 include::layout/split.asciidoc[]
 include::layout/starts_with.asciidoc[]
 include::layout/substring.asciidoc[]