elastic-agent `peak_connections` and `current_connections` are not in _node/stats API vertices response.

[mashhurs]

Logstash information:
Build from main or any latest LS version.

Please include the following information:

1. Logstash version (e.g. bin/logstash --version)
2. Logstash installation source (e.g. built from source, with a package manager: DEB/RPM, expanded from tar or zip archive, docker)
3. How is Logstash being run (e.g. as a service/service manager: systemd, upstart, etc. Via command line, docker/kubernetes)

Plugins installed: (bin/logstash-plugin list --verbose)

JVM (e.g. java -version):

If the affected version of Logstash is 7.9 (or earlier), or if it is NOT using the bundled JDK or using the 'no-jdk' version in 7.10 (or higher), please provide the following information:

1. JVM version (java -version)
2. JVM installation source (e.g. from the Operating System's package manager, from source, etc).
3. Value of the LS_JAVA_HOME environment variable if set.

OS version (uname -a if on a Unix-like system):

Description of the problem including expected versus actual behavior:

Steps to reproduce:

Please include a minimal but complete recreation of the problem,
including (e.g.) pipeline definition(s), settings, locale, etc. The easier
you make for us to reproduce it, the more likely that somebody will take the
time to look at it.

1. Create pipeline with elastic_agent or beats input plugin
2. Run LS and hit localhost:9600/_node/stats?graph=true&vertices=true
3. peak and current connections count were expected to be exist in vertices of the _node/stats API with vertex enabled but they are not

Provide logs (if relevant):