Add "Else If" condition in alert rules

### Problem Statement

Currently, for conditions in the Alert Rule, the flow is `When > If > Then`.
I have some complex alert rules for different features in the codebase.
I want the ability to add an "Else if" rule in Alert Rules so I can route those alerts to appropriate channels in Slack.

### Solution Brainstorm

So, the new flow can look like `When > If > Else If > Then`.

### Product Area

Alerts

### Edit
With ability to add multiple `else if` ladders hopefully