Create consolidated instance destinations table and model

As part of &12339, we need to create tables and models for instance external audit event destinations.

Refrences: POC MR !140362 (closed)

Table structure:

create_table :audit_events_instance_external_streaming_destinations do |t|
t.timestamps_with_timezone null: false
t.text :name, null: false, limit: 72
t.text :type, null: false, limit: 20
t.jsonb :config, null: false
t.binary :encrypted_secret_token, null: false
t.binary :encrypted_secret_token_iv, null: false
end