Restore DayPicker cell sizes to prevent modal overflow

[gally47]

Motivation and Context

fixes https://github.com/Graylog2/graylog-plugin-enterprise/issues/13085
/nocl

related to https://github.com/Graylog2/graylog2-server/pull/23857/changes#diff-fa9643ae0982aab05180b837d119095c2526751559e1e9016b39ebb7847b48b3

Screenshots (if appropriate):

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Refactoring (non-breaking change)
• Breaking change (fix or feature that would cause existing functionality to change)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have requested a documentation update.
• I have read the CONTRIBUTING document.
• I have added tests to cover my changes.

[linuspahl]

Now where the calendar is smaller than the timestamp input, what do you think about centering it again? This is how it looked before the react-day-picker upgrade.

[linuspahl]

Works well, thank you!