[Fleet] Make O11y assistant aware of integration_knowledge* indices for context

[Supplementing]

Summary

Will close https://github.com/elastic/ingest-dev/issues/5680

• Sets the default search connector pattern to match the new system indices of integration_knowledge*. As we support comma separated values for this setting, the user will be able to extend functionality as they see fit.

Open Questions

• If this approach is the correct one, should we consider making it so that this default value of .integration_knowledge* cant be removed by the user if they add other patterns?

Checklist

Check the PR satisfies following conditions.

Reviewers should verify this PR satisfies this list as well.

• Any text added follows EUI's writing guidelines, uses sentence case text and includes i18n support
• Documentation was added for features that require explanation or tutorials
• Unit or functional tests were updated or added to match the most common scenarios
• If a plugin configuration key changed, check if it needs to be allowlisted in the cloud and added to the docker list
• This was checked for breaking HTTP API changes, and any breaking changes have been approved by the breaking-change committee. The release_note:breaking label should be applied in these situations.
• Flaky Test Runner was used on any tests changed
• The PR description includes the appropriate Release Notes section, and the correct release_note:* label is applied per the guidelines
• Review the backport guidelines and apply applicable backport:* labels.

Identify risks

N/A

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[Supplementing]

Currently blocked as we await for elastic/elasticsearch#132506 to get reviewed and merged, and then we can test #230107. Once both are approved/merged, etc then we can manually check that this works as intended and it will be ready for review/CI.

[Supplementing]

Closing for now as there is some work to be done on the ai-assistant side of things. See elastic/elasticsearch#133171 for more context