Updates one or more fields on an existing alert. Only the fields you include in the
request body are changed — omitted fields are left as-is.

Common operations:

• Change parameters: Update thresholds, direction, or other template-specific params. This recompiles the underlying subscription.
• Pause/resume: Set active to false/true.
• Mute temporarily: Set muteUntil to an ISO 8601 timestamp. The alert stays active but suppresses notifications until that time.
• Change delivery: Update connectorIds or callbackUrl.