[ECS] Updating slack to ECS 8.10 & ECS field validation updates

[kgeller]

What does this PR do?

• Updates the slack integration to ECS 8.10
• Correcting ECS categorization fields for validation as a result of Possible regression in field values validation elastic-package#1439

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

• Relates [meta] Upgrade integrations to ECS 8.10 #7480
• Relates Possible regression in field values validation elastic-package#1439

[elasticmachine]

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Build stats

• Start Time: 2023-09-22T17:53:06.563+0000

• Duration: 17 min 12 sec

Test stats 🧪

Test	Results
Failed	0
Passed	5
Skipped	0
Total	5

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[elasticmachine]

🌐 Coverage report

Name	Metrics % (covered/total)	Diff
Packages	100.0% (1/1)	💚
Files	100.0% (1/1)	💚
Classes	100.0% (1/1)	💚
Methods	100.0% (14/14)	💚 2.178
Lines	98.715% (384/389)	👍 11.038
Conditionals	100.0% (0/0)	💚

[elasticmachine]

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

[taylor-swanson]

LGTM

[elasticmachine]

Package slack - 1.12.0 containing this change is available at https://epr.elastic.co/search?package=slack