Set event.type for Packetbeat flow events

[andrewkroh]

What does this PR do?

Add event.type: [connection] to flow events and include end for final flows.

Why is it important?

This helps the data comply to ECS.

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.

Logs

  "event": {
    "type": [
      "connection",
      "end"
    ],
    "start": "2021-03-16T15:14:29.826Z",
    "end": "2021-03-16T15:14:29.826Z",
    "duration": 273694,
    "dataset": "flow",
    "kind": "event",
    "category": [
      "network"
    ],
    "action": "network_flow"
  }

[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)

[botelastic]

This pull request doesn't have a Team:<team> label.

[elasticmachine]

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Build stats

• Build Cause: Pull request #24564 updated

• Start Time: 2021-03-16T15:55:31.248+0000

• Duration: 44 min 45 sec

• Commit: 5599980

Test stats 🧪

Test	Results
Failed	0
Passed	4906
Skipped	45
Total	4951

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Test stats 🧪

Test	Results
Failed	0
Passed	4906
Skipped	45
Total	4951