[Search] Emit errors from EQL search strategy

[rylnd]

Summary

This effectively wraps our EQL strategy in a try/catch, resulting in the observable emitting errors when e.g. the EQL client has an error response. Since the first use case for this strategy involves heavy use of the ignore option, we had not hit this behavior initially.

Checklist

• 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

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 667d7ff

Metrics [docs]

✅ unchanged

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

[elasticmachine]

Pinging @elastic/kibana-app-arch (Team:AppArch)

[yctercero]

This looks great Ryland, thanks so much for the quick fix! Would it be possible to add a mock response for sequences and non sequences here? Not sure if data plugin uses different mock pattern, but thought it could be handy.

[lukeelmers]

Code LGTM!