tools/ocaml: Bump minimum version to OCaml 4.05

Char.lowercase got removed in OCaml 5.0 (it has been deprecated since 2014),
and doesn't build any more.

Char.lowercase_ascii has existed since OCaml 4.03, so that is the new
minimum version for oxenstored.

However, OCaml 4.05 is the oldest new-enough version found in common distros,
so pick this as a baseline.

Signed-off-by: Edwin Török <edwin.torok@cloud.com>
Acked-by: Christian Lindig <christian.lindig@cloud.com>
Acked-by: Anthony PERARD <anthony.perard@citrix.com>
[Update CHANGELOG.md]
Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>

tools/configure

@@ -6836,7 +6836,7 @@ else
                      -e 's/[^0-9]//g'`
 
 
-  ax_compare_version_B=`echo "4.02.0" | sed -e 's/\([0-9]*\)/Z\1Z/g' \
+  ax_compare_version_B=`echo "4.05.0" | sed -e 's/\([0-9]*\)/Z\1Z/g' \
                      -e 's/Z\([0-9]\)Z/Z0\1Z/g' \
                      -e 's/Z\([0-9][0-9]\)Z/Z0\1Z/g' \
                      -e 's/Z\([0-9][0-9][0-9]\)Z/Z0\1Z/g' \