Add curl to the container for healthcheck purposes

[dvanderveer]

Problem

The lemmy.world admins would like to have the ability to perform meaningful health checks in alt UI containers.

Solution

This PR adds curl to the mlmym container for health check purposes.

Testing Done

Confirmed container image build succeeds:

$ docker buildx build -t dvmlmym .
[+] Building 6.6s (21/21) FINISHED                                                                       docker:default
 => [internal] load build definition from Dockerfile                                                               0.0s
 => => transferring dockerfile: 650B                                                                               0.0s
 => [internal] load .dockerignore                                                                                  0.0s
 => => transferring context: 2B                                                                                    0.0s
 => [internal] load metadata for docker.io/library/debian:bullseye-slim                                            0.2s
 => [internal] load metadata for docker.io/library/golang:1.20-bullseye                                            0.2s
 => [builder 1/8] FROM docker.io/library/golang:1.20-bullseye@sha256:74e187ec10d10240e2e88542e75fe8da219d80dade50  0.0s
 => [internal] load build context                                                                                  0.2s
 => => transferring context: 4.08kB                                                                                0.2s
 => [stage-1 1/7] FROM docker.io/library/debian:bullseye-slim@sha256:c618be84fc82aa8ba203abbb07218410b0f5b3c7cb6b  0.0s
 => CACHED [builder 2/8] RUN git config --global --add safe.directory /app                                         0.0s
 => CACHED [builder 3/8] WORKDIR /app                                                                              0.0s
 => CACHED [builder 4/8] COPY go.* ./                                                                              0.0s
 => CACHED [builder 5/8] RUN go mod download                                                                       0.0s
 => [builder 6/8] COPY . ./                                                                                        0.0s
 => [builder 7/8] RUN git describe --tag > VERSION                                                                 0.2s
 => [builder 8/8] RUN go build -v -o mlmym                                                                         5.6s
 => CACHED [stage-1 2/7] WORKDIR /app                                                                              0.0s
 => CACHED [stage-1 3/7] RUN set -x && apt-get update && DEBIAN_FRONTEND=noninteractive apt-get install -y     ca  0.0s
 => [stage-1 4/7] COPY --from=builder /app/mlmym /app/mlmym                                                        0.1s
 => [stage-1 5/7] COPY --from=builder /app/templates /app/templates                                                0.0s
 => [stage-1 6/7] COPY --from=builder /app/public /app/public                                                      0.0s
 => [stage-1 7/7] COPY --from=builder /app/VERSION /app/VERSION                                                    0.0s
 => exporting to image                                                                                             0.1s
 => => exporting layers                                                                                            0.1s
 => => writing image sha256:3fe15e41b87a5a45b796ff66cb91c8459887adcd5df3b656204526b42f0a1424                       0.0s
 => => naming to docker.io/library/dvmlmym                                                                         0.0s

Running the container with a simple curl health check shows the correct health status for both a known-good Lemmy site and a non-existing one:

$ docker run -d -e LEMMY_DOMAIN=lemmy.world --name mlmym_good -p 8080:8080 --health-cmd 'curl -f http://127.0.0.1:8080 || exit 1' dvmlmym
bdbe76dd32e23b6ae0dc1adab1a5b4eebb83a3161587cac582850cdb94877ac0
$ docker run -d -e LEMMY_DOMAIN=doesnt.exist --name mlmym_bad -p 8081:8080 --health-cmd 'curl -f http://127.0.0.1:8080 || exit 1' dvmlmym
067d37bd9f618ddda3d5e1b045e970be7e852256c7d9401c17d0bf02bbccb82d
$ docker ps
CONTAINER ID   IMAGE     COMMAND                  CREATED         STATUS                     PORTS                                       NAMES
067d37bd9f61   dvmlmym   "./mlmym --addr 0.0.…"   2 minutes ago   Up 2 minutes (unhealthy)   0.0.0.0:8081->8080/tcp, :::8081->8080/tcp   mlmym_bad
bdbe76dd32e2   dvmlmym   "./mlmym --addr 0.0.…"   3 minutes ago   Up 3 minutes (healthy)     0.0.0.0:8080->8080/tcp, :::8080->8080/tcp   mlmym_good