[9.3](backport #6419) Implement OTEL secrets replacement in parsed policy

[mergify]

What is the problem this PR solves?

Added functionality to replace secrets in OTEL sections (receivers, exporters, processors, extensions, connectors) of a policy. Updated the NewParsedPolicy function to process these sections and append identified secret keys. Included a new test case to validate the correct replacement of secrets in the OTEL sections.

How does this PR solve the problem?

Add a call to the existing ProcessMapSecrets method for OTEL keys in the policy.

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

• Closes Secrets in Fleet-managed OTel configuration are not rendered #6277

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This is an automatic backport of pull request #6419 done by [Mergify](https://mergify.com).