Pushover Webhook - Test -> OK but notify on Speedtest has no results only {}

[haferm]

Describe the bug
I am using Notification via Webhook to send a message using pushover api.
While the "Test Webhook Channel" works as expected and confirms URL is correct (see also Screenshot) notify on Speedtest has no results. In Message i can see only {} (see 2nd Screenshot)

To Reproduce
Steps to reproduce the behavior:

1.) Test Webhook Channel" sends following message to pushover client:

2.) manual or scheduled speedtest sends following message to pushover client:

Environment (please complete the following information):

• OS: Docker image
• Architecture: amd64
• Browser chrome
• Version 0.19.0

[alexjustesen]

Pushover isn't supported at the moment, the webhook payload happens to be correct when testing but isn't for real payloads. Pushover expects the content in a message param.

Attaching to #40.