Multi Stage Dockerfile to decrease image size

[rblaine95]

Using a multi stage dockerfile results in an image that goes from (on quay) 83.9MB to 19.8MB.
Uncompressed, it goes from 234MB to 50.6MB.

The difference is that XMRig is built on docker build instead of on runtime.

If anyone would like to comment regarding the benefits on this, that would be appreciated.
I like that the image is significantly smaller, however I'm not certain regarding the performance hit.

quay.io/rblaine95/monero_xmrig:latest - larger image, compile on runtime
quay.io/rblaine95/monero_xmrig:tiny - smaller image, compile on build