Document `compat.box_space_max`

[TarantoolBot]

Please create an entry for the new compatibility module option at
https://tarantool.io/compat/box_space_max.

compat.box_space_max sets the max space id (box.schema.SPACE_MAX).
The old limit is 2147483647. The new limit is 2147483646. The limit was
decremented because the old value is used as an error indicator in the
box C API (it equals BOX_ID_NIL).
Requested by @locker in tarantool/tarantool@e529103.

[p7nov]

Add a "see also" link to this doc on the compat.box_space_max descriptions in the configuration reference.