fix: remove built-in image for Docker template (#15504)

The hardcoded image is an anti-pattern, leading to weird errors if the
`docker` group is absent. We should either provide a better error
in-product or just have a better image.

@matifali - also down to use a Devcontainers universal image instead or
make this a parameter. Let me know what you think the best "default
install" is

examples/templates/docker/build/Dockerfile

@@ -1,18 +0,0 @@
-FROM ubuntu
-
-RUN apt-get update \
-	&& apt-get install -y \
-	curl \
-	git \
-	golang \
-	sudo \
-	vim \
-	wget \
-	&& rm -rf /var/lib/apt/lists/*
-
-ARG USER=coder
-RUN useradd --groups sudo --no-create-home --shell /bin/bash ${USER} \
-	&& echo "${USER} ALL=(ALL) NOPASSWD:ALL" >/etc/sudoers.d/${USER} \
-	&& chmod 0440 /etc/sudoers.d/${USER}
-USER ${USER}
-WORKDIR /home/${USER}

examples/templates/docker/main.tf

@@ -169,22 +169,9 @@ resource "docker_volume" "home_volume" {
   }
 }
 
-resource "docker_image" "main" {
-  name = "coder-${data.coder_workspace.me.id}"
-  build {
-    context = "./build"
-    build_args = {
-      USER = local.username
-    }
-  }
-  triggers = {
-    dir_sha1 = sha1(join("", [for f in fileset(path.module, "build/*") : filesha1(f)]))
-  }
-}
-
 resource "docker_container" "workspace" {
   count = data.coder_workspace.me.start_count
-  image = docker_image.main.name
+  image = "codercom/enterprise-base:ubuntu"
   # Uses lower() to avoid Docker restriction on container names.
   name = "coder-${data.coder_workspace_owner.me.name}-${lower(data.coder_workspace.me.name)}"
   # Hostname makes the shell more user friendly: coder@my-workspace:~$