[netflow] Add pipeline tests and move ecs.version to ingest pipeline

[marc-gr]

What does this PR do?

Moves ecs.version to the ingest pipeline and add pipeline tests.

Checklist

• I have reviewed tips for building integrations and this pull request is aligned with them.
• I have verified that all data streams collect metrics or logs.
• I have added an entry to my package's changelog.yml file.
  - [ ] If I'm introducing a new feature, I have modified the Kibana version constraint in my package's manifest.yml file to point to the latest Elastic stack release (e.g. ^7.13.0).

Related issues

• Relates Move Security integrations to GA #961

[elasticmachine]

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

[elasticmachine]

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Build stats

• Build Cause: Branch indexing

• Start Time: 2021-05-24T22:28:43.187+0000

• Duration: 13 min 8 sec

• Commit: 6fcbb12

Test stats 🧪

Test	Results
Failed	0
Passed	91
Skipped	0
Total	91

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