[FEATURE] Return an empty response for getMappings API when there are no aliases applied

[amsiglan]

Is your feature request related to a problem?
When no alias mappings are applied for an index, the GET mappingsView API throws an exception
/_plugins/_security_analytics/mappings?indexName=c*
Response:
{"ok":false,"error":"[security_analytics_exception] No applied aliases found"}

What solution would you like?
Return an empty result instead since it is not an actionable event for the user.

What alternatives have you considered?
N/A

Do you have any additional context?
N/A