sql/current_date.md: new page

Summary

• sql/current_date.md: new page

Address changes from picodata@745e9589

picodata 24.3.0-119-g745e9589

ANSI: F051-06

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• Close #281 (closed)
• Cherry-pick to: 24.4 / 24.3
• Staging:
  • https://docs.binary.picodata.io/picodata/asabirov_add_current_date_function/reference/sql/current_date/
  • https://docs.binary.picodata.io/picodata/asabirov_add_current_date_function/reference/ansi_sql/#mandatory_features
  • https://docs.binary.picodata.io/picodata/asabirov_add_current_date_function/sql_index/