feat: host opentelemetry memory utilization

[rogercoll]

Relevant information

This is adding the memory golden metric definition for hosts monitored by the opentelemetry collector.

Checklist

• I've read the guidelines and understand the acceptance criteria.
• The value of the attribute marked as identifier will be unique and valid.
• I've confirmed that my entity type wasn't already defined. If it is I'm providing an
  explanation above.

Comments

In Linux systems, the resulting value will be different than the one provided by the infra-agent host. The agent uses the MemAvailable and MemTotal fields from /proc/meminfo to compute the memory usage, while the Open Telemetry Collector relies on a sum of some already provided fields. We consider MemAvailable more fine-grained as it is computed in the kernel and it takes into account memory low watermarks.
Issue proposing MemAvailable as a new state for the Open Telemetry Collector: open-telemetry/opentelemetry-collector-contrib#7417

[CLAassistant]

All committers have signed the CLA.