Osquery manager: Update schema and readme for osquery 4.8.0

[aleksmaus]

What does this PR do?

Updates Osquery Manager mapping and readme for osquery 4.8.0

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).

[elasticmachine]

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Build stats

• Build Cause: Pull request #1213 opened

• Start Time: 2021-06-27T04:53:53.219+0000

• Duration: 10 min 7 sec

• Commit: 12af17d

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Passed	1
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Total	1

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