[SO Migrations] Do not allow convertToMultiNamespaceTypeVersion > '8.0.0'

[afharo]

Summary

Resolves #147344.

Checklist

• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios

For maintainers

• This was checked for breaking API changes and was labeled appropriately

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: 20beb63

Metrics [docs]

Unknown metric groups

ESLint disabled in files

id	before	after	diff
osquery	1	2	+1

ESLint disabled line counts

id	before	after	diff
enterpriseSearch	19	21	+2
fleet	61	67	+6
osquery	109	115	+6
securitySolution	445	451	+6
total			+20

Total ESLint disabled count

id	before	after	diff
enterpriseSearch	20	22	+2
fleet	70	76	+6
osquery	110	117	+7
securitySolution	521	527	+6
total			+21

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[afharo]

Closing in favour of #147369