[elastic_agent]: Agent metrics dashboard: "Agent Hostname" filter not working on 8.15

### Integration Name

Elastic Agent [elastic_agent]

### Dataset Name

_No response_

### Integration Version

2.7.6

### Agent Version

8.15.5

### Agent Output Type

elasticsearch

### Elasticsearch Version

8.15.5

### OS Version and Architecture

N/A

### Software/API Version

_No response_

### Error Message

The "Agent Hostname" filter on the "Agent metrics" dashboard does not work.

### Event Original

_No response_

### What did you do?

Opened the _[Elastic Agent] Agent metrics_ dashboard and selected an agent hostname.

### What did you see?

No changes on the data, is kept showing data for all the agents, including components not running on the agent I selected.

I checked the filter with a 9.3 stack and it's exactly the same

### What did you expect to see?

The data correctly filtered, as the dashboard is built to work only with a single agent

### Anything else?

Upgrading the stack to 8.19.14, the latest 8.19, fixed the issue. As the integration is meant to work with 8.15, either it should be fixed or the stack min version updated.