Make env in ImageConfig a map

Fields in CUE were renamed to the lowercase version of Dockerfile instructions.

There's now opportunity to make other fields simpler to use (e.g., healthcheck), this commit is focused on env.

Signed-off-by: Helder Correia <174525+helderco@users.noreply.github.com>

tests/tasks/dockerfile/image_config.cue

@@ -18,8 +18,8 @@ engine.#Plan & {
 				"""
 		} & {
 			config: {
-				Env: ["PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin", "test=foobar"]
-				Cmd: ["/bin/sh", "-c", "/test-cmd"]
+				env: test: "foobar"
+				cmd: ["/bin/sh", "-c", "/test-cmd"]
 			}
 		}
 	}

tests/tasks/pull/pull.cue

@@ -11,8 +11,8 @@ engine.#Plan & {
 		// assert result
 		digest: "sha256:e7d88de73db3d3fd9b2d63aa7f447a10fd0220b7cbf39803c803f2af9ba256b3"
 		config: {
-			Env: ["PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"]
-			Cmd: ["/bin/sh"]
+			env: PATH: "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
+			cmd: ["/bin/sh"]
 		}
 	}
 }

tests/tasks/pull/pull_auth.cue

@@ -20,8 +20,8 @@ engine.#Plan & {
 		// assert result
 		digest: "sha256:c74f1b1166784193ea6c8f9440263b9be6cae07dfe35e32a5df7a31358ac2060"
 		config: {
-			Env: ["PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"]
-			Cmd: ["/bin/sh"]
+			env: PATH: "/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin"
+			cmd: ["/bin/sh"]
 		}
 	}
 }

tests/tasks/push/push.cue

@@ -42,7 +42,7 @@ engine.#Plan & {
 		push: engine.#Push & {
 			dest:  "daggerio/ci-test:\(randomString.output)"
 			input: randomString.image.output
-			config: Env: ["FOO=\(randomString.output)"]
+			config: env: FOO: randomString.output
 			auth: #auth
 		}
 
@@ -54,9 +54,7 @@ engine.#Plan & {
 			// check digest
 			digest: strings.Split(push.result, "@")[1]
 			// check image config
-			config: {
-				Env: ["FOO=\(randomString.output)"]
-			}
+			config: env: FOO: randomString.output
 		}
 
 		pullOutputFile: engine.#ReadFile & {