Fix typo in max number of threads check docs (#29469)

Historically, the bootstrap checks used 2048 as the minimum limit for
the maximum number of threads. This limit was guided by the fact that
the number of processors was artificially capped at 32. This limit was
removed in 6.0.0 and the minimum limit was raised to 4096 to accommodate
this. However, the docs were not updated and this commit addresses that
miss.

Author: sachinfrayne

docs/reference/setup/bootstrap-checks.asciidoc

@@ -114,7 +114,7 @@ that the Elasticsearch process has the rights to create enough threads
 under normal use. This check is enforced only on Linux. If you are on
 Linux, to pass the maximum number of threads check, you must configure
 your system to allow the Elasticsearch process the ability to create at
-least 2048 threads. This can be done via `/etc/security/limits.conf`
+least 4096 threads. This can be done via `/etc/security/limits.conf`
 using the `nproc` setting (note that you might have to increase the
 limits for the `root` user too).