[Fleet Integration]: Create a default dedicated ILM policy for fleet internal data streams and expose a configurable retention period in Fleet UI

### Integration Name

Fleet Server [fleet_server]

### Dataset Name

fleet_server.agent_versions, fleet_server.agent_status

### Integration Version

1.6.0

### Agent Version

9.2.4

### OS Version and Architecture

Ubuntu 20.04

### User Goal

Expose configuration for retention of internal fleet datasets in Fleet UI, to have a dedicated ILM policy for those data streams

### Existing Features

The retention period for fleet internal data streams is not clearly exposed in the Fleet UI, today the end user needs to go all the way to index management, data streams to figure that those are using the metrics default ILM policy.

### What did you see?

1. The retention config that those data streams use (ILM in this case) should be clearly informed in Fleet UI.
2. The default metrics ILM policy is also used by many metrics integrations that the end user might be using, changing retention there would affect all of the metrics leveraging it.

### Anything else?

_No response_