[Metadata] No dependency check for support-notifications on startup

[tonyespy]

Core Metadata has a notifications feature used to trigger notifications when devices are added. This feature is enabled by default and configured via the [Notifications] configuration stanza:

[Notifications]
PostDeviceChanges = true
Content = "Meatadata notice: "
Sender = "core-metadata"
Description = "Metadata change notice"
Label = "metadata"

Since the edgexfoundry snap disables support-notifications by default (as by there are no subscriptions configured)**, when devices are added, the follow error message is logged:

level=ERROR ts=2021-10-21T19:26:14.081557524Z app=core-metadata source=notify.go:53 msg="fail to invoke device service callback for adding device test-device-3, err: request failed, status code: 500, err: {\"apiVersion\":\"v2\",\"message\":\"driver.AddDevice callback failed for test-device-3 -\\u003e error adding device: ONVIF client could not be initialized: test-device-3\",\"statusCode\":500}"

Note, if the device being added defines secrets, then these need to be added before the device is added, as the call to notify support-notifications only happens if enabled and the callback to the device service succeeds.

If this Notifications.Enabled=true, then Core Metadata should check (via go-mod-bootstrap) that Support Notifications is available on startup.

Steps to reproduce

Note, these steps could be simplified by using a different device-service snap which doesn't require secrets, but this is how I managed to reproduce this today.

add-camera-secrets.sh:

#!/bin/sh

curl -w %{http_code} -X POST \
-d '{
  "apiVersion": "2",
  "path" : "credentials001",
  "secretData" : [
    {
      "key" : "username",
      "value" : "admin"
    },
	{
      "key" : "password",
      "value" : "ADMIN"
    }
  ]
}' http://localhost:59985/api/v2/secret

On an Ubuntu system:

$ sudo snap install edgexfoundry --channel=2.0
$ sudo snap install edgex-device-camera --channel=2.0
$ sudo snap start --enable edgex-device-camera.device-camera
$ ./add-camera-secrets.sh
$ sudo journalctl -f -o cat

The last command will display system logs continuously until you exit via Ctrl-C.

Use the UI to a device:

$ sudo snap install edgex-ui --edge
Now open the UI in a browser using the URL: http://localhost:4000, and add a device to the device-camera service using the following values:

Name = "Camera001"
ProfileName = "camera"
Description = "tony camera"
Location = "brickbottom"
  [DeviceList.Protocols]
    [DeviceList.Protocols.HTTP]
    Address = "192.168.0.13:8080"
    AuthMethod = "usernamepassword"
    CredentialsPath = "credentials001"

** We also should consider disabling this notifications by default, as it makes no sense to send a notification to Support Notifications unless someone has explicitly created at least a single subscription for this event.

Version: 2.0.1-dev.68
Deployment: snap

[cloudxxx8]

We discussed a little in the Core WG meeting on OCT-21-2021.
It might be better to set the default to false.
However, the dependency check would block the core-metadata starting up. @siggiskulason suggested we can replace the Error messages with Warning messages.
Thus the changes are proposed for this issue are:

1. Set the default value to disable sending out notifications
2. Modify the log level to Warning instead of Error when the Notifications sending fails
   Note: Not adding dependency check

@tonyespy is it ok for you?

If so, @jinlinGuan we would need to modify TAF test, too