Fix incorrect statement about Lucene's default operator

[Bargs]

Summary

Fixes #50048

Lucene uses or as its default operator, so response:200 extension:php would become response:200 or extension:php.

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

[Bargs]

@gchaps do you have any tricks to make backporting docs changes to a ton of branches less painful? 😅

[elasticmachine]

💚 Build Succeeded

• continuous-integration/kibana-ci/pull-request
• Commit: 67cbdfb

[gchaps]

LGTM.

Use yarn backport-skip-ci to make the backporting go faster.