Migrate Netflow code to the logp logging library

[jrmolin]

Proposed commit message

[Netflow] Migrate from log to the logp logging library

• The rest of beats is using github.com/elastic/elastic-agent-libs/logp, so make Netflow use it, too.
• Cleaned up the test code as well

Checklist

• My code follows the style guidelines of this project
• 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.next.asciidoc or CHANGELOG-developer.next.asciidoc.

Disruptive User Impact

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Implementation Detail: Logging should use logp everywhere #42247

Use cases

Screenshots

Logs

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)

[elasticmachine]

Pinging @elastic/sec-deployment-and-devices (Team:Security-Deployment and Devices)

[stefans-elastic]

just curious - why is this PR to branch 8.x and not main?

[jrmolin]

I was trying to get this into 8.18, @stefans-elastic

[jrmolin]

what should I do now?

[andrewkroh]

It looks like the code doesn't build successfully at the moment.

This PR should target the main branch, then automation will open a PR to backport this into the 8.x branch if you have applied the backport-8.x label.

[andrewkroh]

LGTM. But the PR must go through main then we will backport it into 8.x via automation. You should be able to edit the target branch (and I assume a rebase would be needed).

[jrmolin]

closing in favor of #42704, which targets main