refactor: restore parameterless NewFactory functions for Beat receivers

[andrzej-stencel]

To keep them compatible with OpenTelemetry Collector Builder.

Proposed commit message

Restores parameterless NewFactory functions for Filebeat receiver and Metricbeat receiver to keep their API compatible with OpenTelemetry Collector Builder, which requires parameterless NewFactory function.

The function NewFactoryWithSettings(Settings) has been introduced for use in the Elastic Agent to inject settings in runtime.

• Relates NewFactory for beatreceivers takes default home and data dirs #49327

• Relates [beats receivers] Using Filebeat modules or Metricbeat lightweight modules requires manually setting home path to the components directory elastic-agent#11734

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. Where relevant, I have used the stresstest.sh script to run them under stress conditions and race detector to verify their stability.
• I have added an entry in ./changelog/fragments using the changelog tool.

[github-actions]

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[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)

[coderabbitai]

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ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Organization UI

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Plan: Pro

Run ID: 2c9e14c1-170c-4ccb-9e4a-c851052d9f3f

📥 Commits

Reviewing files that changed from the base of the PR and between eff0889 and c249d71.

📒 Files selected for processing (8)

• changelog/fragments/1773087971-change-beat-receiver-factory-to-have-default-home-and-path-directories.yaml
• x-pack/filebeat/fbreceiver/factory.go
• x-pack/filebeat/fbreceiver/receiver_leak_test.go
• x-pack/filebeat/fbreceiver/receiver_test.go
• x-pack/metricbeat/mbreceiver/factory.go
• x-pack/metricbeat/mbreceiver/receiver_leak_test.go
• x-pack/metricbeat/mbreceiver/receiver_test.go
• x-pack/otel/oteltestcol/collector.go

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📝 Walkthrough

Walkthrough

Refactored receiver factory constructors across filebeat and metricbeat modules. Renamed the existing parameterized factory functions to NewFactoryWithSettings() and added new parameterless NewFactory() functions that instantiate factories with default empty settings. Updated all corresponding test files and a test collector to call the appropriate factory variant—NewFactoryWithSettings() when custom settings are required, and NewFactory() for default configurations. Updated changelog metadata accordingly.

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• Create PR with unit tests

• 🛠️ Update Documentation: Commit on current branch
• 🛠️ Update Documentation: Create PR

📝 Coding Plan

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