feat: support service.command

This patch extends dcmerge to support the command attribut of a defined service.
For example:

```yaml
services:
  busybox
    command: [ "/usr/bin/cp", "--recursive", "--force", "/tmp/bar.txt", "/tmp/foo.txt"]
    image: library/busybox:latest
```

The command attribute is interpreted as a whole. This means that individual
arguments are not merged as a comparison, as this would change the meaning of
the command attribute.

pkg/domain/dockerCompose/test/assets/merge/testcase003/docker-compose-000.yml

@@ -0,0 +1,4 @@
+services:
+  frontend:
+    command: [ "/usr/bin/cp", "--recursive", "--force", "/tmp/foo.txt", "/tmp/bar.txt" ]
+    image: library/frontend:latest

pkg/domain/dockerCompose/test/assets/merge/testcase003/docker-compose-001.yml

@@ -0,0 +1,4 @@
+services:
+  frontend:
+    command: [ "/usr/bin/cp", "--recursive", "--force", "/tmp/bar.txt", "/tmp/foo.txt"]
+    image: library/frontend:latest

pkg/domain/dockerCompose/test/assets/merge/testcase003/expectedResult.yml

@@ -0,0 +1,8 @@
+services:
+  backend:
+    image: library/backend:latest
+  frontend:
+    depends_on:
+      backend:
+        condition: service_completed_successfully
+    image: library/frontend:latest