Event Grid: Add MonitorAlert support and delivery schema configuration

[MartinWa]

This PR closes #1255

The changes in this PR are as follows:

• Update Event Grid API version to 2025-02-15.
• Add MonitorAlert endpoint type for event subscriptions.
• Support action groups and severity levels (Sev0–Sev4) for alerts.
• Add event_delivery_schema keyword for schema selection.

I have read the contributing guidelines and have completed the following:

• Tested my code end-to-end against a live Azure subscription.
• Updated the documentation in the docs folder for the affected changes.
• Written unit tests against the modified code that I have made.
• Updated the release notes with a new entry for this PR.
• Checked the coding standards outlined in the contributions guide and ensured my code adheres to them.

Below is a minimal example configuration that includes the new features, which can be used to deploy to Azure:

open Farmer
open Farmer.Builders
open Farmer.Arm.EventGrid

let alertGroup = actionGroup {
    name "myActionGroup"
    short_name "myAG"
}

let keyVault = keyVault {
    name "myKeyVault"
}

let eventGridTopic = eventGrid {
    topic_name "kv-expiry-topic"
    source keyVault
    event_delivery_schema CloudEventSchemaV1_0

    add_monitor_alert_subscriber
        [ alertGroup ]
        Sev3
        [ SystemEvents.KeyVault.SecretNearExpiry ]
}

let deployment = arm {
    add_resource alertGroup
    add_resource keyVault
    add_resource eventGridTopic
}