[Explore vis] Fix discover vis Y-Axis not display caused by crosshair axis setting (#10809)

Fix Y-Axis not display caused by crosshair axis setting, the `axis: null` will hide the entire axis, changed to `axis.title: ''` to not display the default title which is the field name

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Signed-off-by: Yulong Ruan <[email protected]>
Co-authored-by: opensearch-changeset-bot[bot] <154024398+opensearch-changeset-bot[bot]@users.noreply.github.com>

Author: ruanyl

changelogs/fragments/10809.yml

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+fix:
+- Discover vis Y-Axis not display caused by crosshair axis setting ([#10809](https://github.com/opensearch-project/OpenSearch-Dashboards/pull/10809))