[Enhancement] Package spec should expose a flag if the integration can be run on EA standalone or not + supported outputs

The package spec should be enhanced to expose 2 informations:
- If the integration can be used on Elastic Agent standalone or not. Examples:
- APM Integration https://github.com/elastic/apm-server/issues/6921
- Synthetics integration https://www.elastic.co/guide/en/observability/current/synthetics-private-location.html#:~:text=Private%20Locations%20cannot%20be%20set%20up%20using%20standalone%20Elastic%20Agents
- The list of supported outputs per integration. Examples:
- APM integration only supports Elasticsearch
- Fleet Server integration only supports Elasticsearch
- Synthetics (Private Locations) integration only supports Elasticsearch https://www.elastic.co/guide/en/observability/current/synthetics-private-location.html#:~:text=Private%20Locations%20running%20through%20Elastic%20Agent%20must%20have%20a%20direct%20connection%20to%20Elasticsearch
- Elastic Defend supports Elasticsearch, Logstash, Kafka (since 8.12)

The information can be used in docs and in the future by Fleet UI in some situations.