[Metric Alerts] Add event.type:csp as an event filter option.

### Problem Statement

Currently, in metric alerts, there are only options for `event.type:error` and `event.type:default` and no way to alert based on the csp type.

Specfic customer feedback:
_I think being able to build an alert saying I got more than X CSP events in Y time frame would be very useful if an attacker is trying a bunch of attacks that are generating CSP violations._

### Solution Brainstorm

Ability to add `event.type:csp` as an option in the dropdown.