Add destination.domain field to alert mapping

[ricardo-estc]

Change Summary

Add destination.domain field part of alert mapping

Sample values

Sample document:

Release Target

This should be merged in main and backported to 9.1 and 8.19 if possible

Q/A

For mapping changes:

• I ran make after making the schema changes, and committed all changes
• If these field(s) are "exception"-able, I made a companion PR to Kibana adding it (see Readme)
• If this is a metadata change, I also updated both transform destination schemas to match

For Transform changes:

• The new transform successfully starts in Kibana
• The corresponding transform destination schema was updated if necessary