Add parameters and payload in Observability Alert Webhooks

[AlexeySumin]

Feature request for /observability/alerts/add
You might want to use a webhook to send an http request somewhere. But functionality of webhooks in OM is not enought, beacause a lot of services want you to send payload.

TO BE:

1. It is possible to add parameters in Advanced configuration, like in Postman
2. It is possible to add a payload in Advanced configuration, like in Postman