[OTel] Add ContainerMetricsReceiver

[sean-breen]

Proposed changes

Adds a new receiver to collect container metric from inside a container, by reading the files under cgroup directory. This PR will add the receiver and a basic CPU and Memory metric, however these need to be expanded on to provide more value for users.

The receiver aims to support cgroup V1 and V2.

The receiver can be enabled in the agent config by specifying the container_metrics as a receiver under the OTel configuration.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING document
• I have run make install-tools and have attached any dependency changes to this pull request
• If applicable, I have added tests that prove my fix is effective or that my feature works
• If applicable, I have checked that any relevant tests pass after adding my changes
• If applicable, I have updated any relevant documentation (README.md)
• If applicable, I have tested my cross-platform changes on Ubuntu 22, Redhat 8, SUSE 15 and FreeBSD 13

[sean-breen]

Closing this for now as more fundamental changes are needed after discussing with Donal