config: add StopSignal

Signed-off-by: Antonio Murdaca <runcom@redhat.com>

config.md

@@ -124,6 +124,10 @@ Note: Any OPTIONAL field MAY also be set to null, which is equivalent to being a
      If there are no labels then this property MAY either be absent or an empty map.
      Implementations that are reading/processing this configuration file MUST NOT generate an error if they encounter an unknown labels key.
 
+  - **StopSignal** *string*, OPTIONAL
+
+    The field contains the system call signal that will be sent to the container to exit. The signal can be a valid unsigned number that matches a position in the kernel’s syscall table, for instance `9`, or a signal name in the format `SIGNAME`, for instance `SIGKILL`.
+
 - **rootfs** *object*, REQUIRED
 
    The rootfs key references the layer content addresses used by the image.

schema/config-schema.json

@@ -80,6 +80,9 @@
               "type": "null"
             }
           ]
+        },
+        "StopSignal": {
+          "type": "string"
         }
       }
     },

schema/config_test.go

@@ -164,6 +164,7 @@ func TestConfig(t *testing.T) {
             "/var/job-result-data": {},
             "/var/log/my-app-logs": {}
         },
+        "StopSignal": "SIGKILL",
         "WorkingDir": "/home/alice",
         "Labels": {
             "com.example.project.git.url": "https://example.com/project.git",