Use alpine as base image

[ismith]

Alpine is not that much bigger than google's distroless image. and
having this OS layer underneath will make it easier to debug.

(Currently: do we have a problem with the network interface name in our
config?)

[ismith]

Test: run ./build-docker.sh, output contains:
2021/11/01 16:34:23 Using base alpine:3.13 for github.com/honeycombio/refinery/cmd/refinery

[Vlaaaaaaad]

I am very much in favour of this (it'll also make it easier to run Refinery using ECS on Fargate, related Slack thread here), but any chance something other than Alpine can be used?

Alpine is somewhat well known to have runtime issues due to musl. I had massive DNS issues in Kubernetes due to this, so I am now hyper-aware, even if some bugs were fixed.

Compared to Alpine's 2MB size, alternatives are indeed ten times bigger with Ubuntu images being ~27MB and Debian slim images being ~22MB, but I think the added size has minimal impact.

[MikeGoldsmith]

I'm good with changing the default image to alpine.

@ismith do you have an opinion on @Vlaaaaaaad's recommendation regarding Ubuntu/Debian images instead?

[MikeGoldsmith]

@Vlaaaaaaad I'm going to merge this PR using alpine as base image. Please raise an issue if you feel you'd still like use to consider us using another base image.