Run compsvc on CompOS boot

Bug: 186126809
Test: 1. follow microdroid/README.md except payload.img:
        $ adb shell 'cd /data/local/tmp/microdroid;    \
           /apex/com.android.virt/bin/mk_payload       \
           /apex/com.android.compos/etc/payload_config.json \
           payload.img'
	$ adb shell 'chmod go+r /data/local/tmp/microdroid/payload*'
      2. adb shell /apex/com.android.virt/bin/vm run \
           /data/local/tmp/microdroid/microdroid.json

Change-Id: I03cc937c0f82cbcc4fd1064ce2135619f22b4170
diff --git a/compos/payload_config.json b/compos/payload_config.json
new file mode 100644
index 0000000..588ccca
--- /dev/null
+++ b/compos/payload_config.json
@@ -0,0 +1,15 @@
+{
+  "apk": {
+    "path": "/apex/com.android.compos/app/CompOSPayloadApp/CompOSPayloadApp.apk",
+    "name": "com.android.compos.payload"
+  },
+  "system_apexes": [
+    "com.android.adbd",
+    "com.android.art",
+    "com.android.compos",
+    "com.android.i18n",
+    "com.android.os.statsd",
+    "com.android.sdkext"
+  ],
+  "payload_config_path": "/mnt/apk/assets/vm_config.json"
+}
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