Fix max number of threads bootstrap docs

Previously the bootstrap check for max number of threads was increased
from 2048 to 4096 yet the docs were never adjusted for this change. This
commit addresses this so the docs are in-line with the limit enforced in
the bootstrap check.

Relates #27511

docs/reference/setup/sysconfig/threads.asciidoc

@@ -4,9 +4,9 @@
 Elasticsearch uses a number of thread pools for different types of operations.
 It is important that it is able to create new threads whenever needed.   Make
 sure that the number of threads that the Elasticsearch user can create is at
-least 2048.
+least 4096.
 
-This can be done by setting <<ulimit,`ulimit -u 2048`>> as root before
-starting Elasticsearch, or by setting `nproc` to `2048` in
+This can be done by setting <<ulimit,`ulimit -u 4096`>> as root before
+starting Elasticsearch, or by setting `nproc` to `4096` in
 <<limits.conf,`/etc/security/limits.conf`>>.