OpAMP redact slice maps

[michel-laterman]

What is the problem this PR solves?

Redact slice maps with the form:

- name: Authorization
  value: secretValue

How does this PR solve the problem?

Use the shared redact package in elastic-agent-libs

How to test this PR locally

Enroll an opamp agent with sensitive values in the headers slices.

Design Checklist

• I have ensured my design is stateless and will work when multiple fleet-server instances are behind a load balancer.
• I have or intend to scale test my changes, ensuring it will work reliably with 100K+ agents connected.
• I have included fail safe mechanisms to limit the load on fleet-server: rate limiting, circuit breakers, caching, load shedding, etc.

Checklist

• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have made corresponding change to the default configuration files
• I have added tests that prove my fix is effective or that my feature works
• I have added an entry in ./changelog/fragments using the changelog tool

Related issues

• Relates Move secret redaction logic to elastic-agent-libs elastic-agent-libs#415