LIKE, ILIKE, LOWER/UPPER

Summary

• like.md: new document
• ilike.md: new document
• lower_upper.md: new document

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• Close #347 (closed), #356 (closed)
• Cherry-pick to: none
• Staging:
  • https://docs.binary.picodata.io/picodata/at_sql_like/reference/sql/like/
  • https://docs.binary.picodata.io/picodata/at_sql_like/reference/sql/ilike/
  • https://docs.binary.picodata.io/picodata/at_sql_like/reference/sql/lower_upper/