feat: Docker container

[cpustejovsky]

• move cli code into discrete package and update imports
• create Dockerfile

This work I did leads to this error while trying to build the image:

$ docker build -f Dockerfile .
Sending build context to Docker daemon  12.74MB
Step 1/7 : FROM golang:1.18-alpine
 ---> f37f1bcb329f
Step 2/7 : WORKDIR /app
 ---> Using cache
 ---> 1766b732707c
Step 3/7 : COPY go.mod ./
 ---> Using cache
 ---> 8297ec26d0c6
Step 4/7 : RUN go mod download
 ---> Using cache
 ---> 5fd3d73878aa
Step 5/7 : COPY . .
 ---> 3366be268b66
Step 6/7 : RUN go build -o cli cmd/cli/main.go
 ---> Running in 718c17c5fc78
# github.com/go-gl/glfw/v3.3/glfw
cgo: C compiler "gcc" not found: exec: "gcc": executable file not found in $PATH
# pkg-config --cflags  -- gl gl
pkg-config: exec: "pkg-config": executable file not found in $PATH
The command '/bin/sh -c go build -o cli cmd/cli/main.go' returned a non-zero code: 2

I looked around and attempted solution but this is where I got stuck. Leaving here in case someone wants to continue the work one of the repo's TODO items.