test: add scheduler-k3s run parity tests across builders

Extends bats coverage for the scheduler-k3s scheduler so that
herokuish and dockerfile builders match the cnb test surface for
`dokku run`, `dokku run:detached`, `dokku cron:run`, deployment
manifests, cronjob manifests, and Procfile-key resolution. Adds
the corresponding `app-cron-procfile.json` fixture for the python
app and `app-cron.json` / `app-cron-procfile.json` fixtures for
the dockerfile-procfile app.

tests/apps/python/app-cron-procfile.json

@@ -0,0 +1,21 @@
+{
+  "cron": [
+    {
+      "command": "task",
+      "schedule": "5 5 5 5 5"
+    }
+  ],
+  "healthchecks": {
+    "web": [
+      {
+        "attempts": 2,
+        "content": "python/http.server",
+        "name": "check-1",
+        "path": "/",
+        "timeout": 5,
+        "type": "startup",
+        "wait": 2
+      }
+    ]
+  }
+}