[Beats CM] Fix beat list redirect to welcome page

[justinkambic]

Summary

At the moment, the search bar on the beats list page will redirect the user if the filter endpoint returns an empty set:

This change adds a new state field, unfilteredBeats, that contains all the beats. The logic for determining when to redirect now checks this field instead of the beats field, which is subject to filtering.

Checklist

Use strikethroughs to remove checklist items you don't feel are applicable to this PR.

- [ ] This was checked for cross-browser compatibility, including a check against IE11
- [ ] 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
- [ ] This was checked for keyboard-only and screenreader accessibility

For maintainers

• This was checked for breaking API changes and was labeled appropriately
• This includes a feature addition or change that requires a release note and was labeled appropriately

[elasticmachine]

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• continuous-integration/kibana-ci/pull-request