Add support for with_fields configuration

[khushijain21]

What does this PR do?

It adds with_fields config to logging section - which allows for additional structured context to the logs emitted by beat process
For https://github.com/elastic/ingest-dev/issues/5139

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

Related issues

• Part of https://github.com/elastic/ingest-dev/issues/5139

[khushijain21]

The docs are not updated with this config because it is introduced to solve an internal problem and is kept private initially.

[khushijain21]

/test

[khushijain21]

/test

[elasticmachine]

💚 Build Succeeded

• Buildkite Build
• Commit: 25a89d3

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• 💔 Build #632 failed 5316f7f
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