[Feature] Collect cloud metadata

Add collection for cloud metadata -- see [naive example here](https://github.com/hubblestack/hubble/blob/develop/hubblestack/extmods/grains/cloud_details.py)

APM Server will support intake for cloud metadata in 7.8 (now available in nightly snapshots).

**Additional context**

https://github.com/elastic/apm/issues/256