tenable_sc: add mapping for event.created

[efd6]

What does this PR do?

This adds an ECS type mapping for the event.created field.

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.

Author's Checklist

• [ ]

How to test this PR locally

Related issues

• Closes tenable_sc: no mapping for event.created #3567

Screenshots

[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: 2022-06-23T03:48:46.382+0000

• Duration: 17 min 56 sec

Test stats 🧪

Test	Results
Failed	0
Passed	38
Skipped	0
Total	38

🤖 GitHub comments

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

• /test : Re-trigger the build.

[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (3/3)	💚
Files	100.0% (3/3)	💚 3.448
Classes	100.0% (3/3)	💚 3.448
Methods	100.0% (41/41)	💚 11.199
Lines	96.852% (923/953)	👍 6.909
Conditionals	100.0% (0/0)	💚