Gotify agent alert notifications

Gotify is a self-hosted push notification service created for sending and receiving messages in real time.

Configuring Gotify

To use Gotify as your notification service, you need an application token. You can generate a new token in the Gotify Web UI.

To set up Gotify in Netdata:

Switch to your config directory and edit the file health_alarm_notify.conf using the edit config script.
```
./edit-config health_alarm_notify.conf
```
Change the variable GOTIFY_APP_TOKEN to the application token you generated in the Gotify Web UI. Change GOTIFY_APP_URL to point to your Gotify instance.
```
SEND_GOTIFY="YES"

# Application token
# Gotify instance url
GOTIFY_APP_TOKEN=XXXXXXXXXXXXXXX
GOTIFY_APP_URL=https://push.example.de/
```
Changes to health_alarm_notify.conf do not require a Netdata restart.
Test your Gotify notifications configuration by running the following commands, replacing ROLE with your preferred role:
```
# become user netdata
sudo su -s /bin/bash netdata

# send a test alarm
/usr/libexec/netdata/plugins.d/alarm-notify.sh test ROLE
```
🟢 If everything works, you'll see alarms in Gotify:
🔴 If sending the test notifications fails, check /var/log/netdata/error.log to find the relevant error message:
```
2020-09-03 23:07:00: alarm-notify.sh: ERROR: failed to send Gotify notification for: hades test.chart.test_alarm is CRITICAL, with HTTP error code 401.
```