Support for external configurations under inputs.d was introduced with 3c2072d . However the documentation around this is not quite helpful and it is only mentioned at https://www.elastic.co/guide/en/fleet/8.2/elastic-agent-configuration.html as you can put input configurations in YAML files into the folder {path.config}/inputs.d.

However this is not quite trivial to use this in container environments and even trying several different combinations didn't work.
I tried putting the inputs.d as /usr/share/elastic-agent/state/inputs.d, as /etc/elastic-agent when running with -c /etc/elastic-agent/elastic.yml and as /usr/share/elastic-agent/inputs.d but nothing works and logs don't provide any useful insight.

Note that Agent directory is under /usr/share/elastic-agent and it is started with -c /etc/elastic-agent/agent.yml.

cat container-paths.yml 
state_path: /usr/share/elastic-agent/state
config_path: /usr/share/elastic-agent/state

Find a complete k8s manifest below:
elastic-agent-standalone-kubernetes.yaml.txt

@ph could we have some help on clarifying those please?
cc: @gizas

This is important for #662.
Also related to #622.