Add mappings on .fleet-policies index to filter on data.outputs to invalidate remote API keys

[juliaElastic]

Related to elastic/kibana#104986
Follow up after #3051 (comment)

Currently data.outputs in .fleet-policies is not mapped, so we can't use ES query to find a remote output config after it is removed from an agent/agent policy. We need the config to invalidate remote API keys that are not used anymore.

Currently the logic looks up the most recent policy revisions and loops though them to find the remote output. This is not efficient and might not return the output config.

To solve this:

• Add ES mapping for data.outputs, to be able to search on a remote output ID
  • We should check if changing the mapping doesn't break existing clusters when migrating to a new version. Alternatively a new field name could be used for the new mapping.

 "data": {
          "enabled": false,
          "type": "object"
        },

• Change the implementation in fleet-server to query on output in ES.