Update elasticstack_fleet_output resource to use new API schema types

[taylor-swanson]

Starting in fleet/kibana API version 8.10.0, the fleet output types have been updated to use more strongly typed data structures to hold the output configuration. The elasticstack_fleet_output resource type will need to be updated to support these different structures. This issue will handle supporting the elasticsearch and logstash types (in general, already supported by the resource) and will lay the foundation to allow kafka to be added in the future (see #395).