[Doc] update the example of using central pipeline management

[kaisecheng]

Tell us about the issue

The privileges listed in the examples are outdated or giving syntax error.

Description:
To use CPM, we need two cluster privileges manage_logstash_pipelines and monitor
The role logstash_admin is not enough to use CPM as it misses monitor to query /_xpack which is a necessary call to use xpack features

URL:

Granting access to the Logstash indices
https://www.elastic.co/guide/en/logstash/8.17/ls-security.html#ls-user-access

Create an API key for central management
https://www.elastic.co/guide/en/logstash/8.17/ls-security.html#ls-api-key-man

Configuration Management Settings in Logstash
https://www.elastic.co/guide/en/logstash/current/configuring-centralized-pipelines.html

Anything else?