Add event.created field mapping to TI packages

[P1llus]

What does this PR do?

This adds events.created to the ecs.yml field mapping file for TI packages.

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.
• I have verified that Kibana version constraints are current according to guidelines.

[elasticmachine]

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

[elasticmachine]

💚 Build Succeeded

the below badges are clickable and redirect to their specific view in the CI or DOCS

Expand to view the summary

Build stats

• Start Time: 2022-04-11T10:08:30.611+0000

• Duration: 14 min 1 sec

Test stats 🧪

Test	Results
Failed	0
Passed	77
Skipped	0
Total	77

🤖 GitHub comments

To re-run your PR in the CI, just comment with:

• /test : Re-trigger the build.

[P1llus]

/test