Report FIPS-capability in ListAgentsResponse

[ycombinator]

What does this PR do?

The ListAgentsResponse method on the Kibana Fleet client returns a list of Agents. This PR adds a new LocalMetadata.Elastic.Agent.FIPS boolean field to each Agent in the list.

Why is it important?

So consumers of the ListAgentsResponse API, e.g. tests, can check if the returned Agents are FIPS-capable or not.

Checklist

• My code follows the style guidelines of this project
• I have commented my code, particularly in hard-to-understand areas
• I have added tests that prove my fix is effective or that my feature works

[elasticmachine]

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