[Cloud Posture] Cloudbeat logs fields update

[oren-zohar]

What does this PR do?

adds explicit mapping for the message fields to support cloudbeat logs searching.

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.

Related issues

• Closes [BUG] Filtering cloudbeat logs on Agent Logs page yields no results cloudbeat#170
• Relates [Fleet] ECS fields in packages are not included in index.query.default_field setting #3926

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• Start Time: 2022-08-01T15:07:03.993+0000

• Duration: 14 min 16 sec

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Test	Results
Failed	0
Passed	32
Skipped	0
Total	32

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🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (0/0)	💚
Files	100.0% (0/0)	💚 2.868
Classes	100.0% (0/0)	💚 2.868
Methods	33.333% (22/66)	👎 -55.917
Lines	100.0% (0/0)	💚 9.394
Conditionals	100.0% (0/0)	💚