RAM capacity metric

[bpetit]

Problem

Higher level environmental impact calculation tools like Boagent or SoftAWARE estimate the embodied impacts (raw material extraction, manufacturing, transport, end of life) of a machine. Scaphandre is already a building block for those tools and it only lacks a few metrics to simplify the whole stack (so we don't need to many extra exporters like node_exporter while using only 1% of its metrics). In a broader way, having such metrics as RAM capacity can be helpful to use embodied impacts calculation tools like BoaviztAPI.

Solution

Add total RAM capacity of the machine to Scaphandre metrics. Could be scaph_ram_total.