Compose files are missing "pid: host" param for agent

[zeldigas]

While current example works, they are pretty simple. While trying to try more proper use case - agent is in it's own container and workload in it's dedicated one with docker selector, I spent a lot of time figuring one why I got error

could not resolve caller information

After some trial, error and googling around I found similar thing about k8s and indeed putting mentioned param did the trick

  spire-agent:
    image: gcr.io/spiffe-io/spire-agent:0.12.0
    depends_on: ["spire-server"]
    hostname: spire-agent
    pid: host

Not sure if it should go to this repo or spire itself, but just FYI

UPD: After additional check, I see that "nested" example contains this flag. The problem is that it's easy to skip in docs (at least while reading about it, I did not find it, maybe worth putting admonition to docker attestor page) and in other examples it's missing (e.g. in telemetry)