[Lens] Make field stats work for index patterns without time fields

[timroes]

Summary

Fix #55033

Currently Lens doesn't allow showing field stats for an index pattern without a time field (the request fail the validation, since no timeField parameter is passed).

This allows also requesting field stats without a timeField, so it will work for those index patterns.

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]

Pinging @elastic/kibana-app (Team:KibanaApp)

[wylieconlon]

Did not test, but this is almost identical to the change I did for the field existence endpoint.

The only thing you could add is a unit test to verify that the correct request is made from the client in this case.

[kibanamachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: a985467

History

• 💛 Build #24616 was flaky d5ee4fe
• 💚 Build #24600 succeeded fd6f108
• 💚 Build #24340 succeeded a6c5aa8

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