`SqlCatalog._namespace_exists()` should use `LIKE` instead of an exact match on the namespace

[alessandro-nori]

Apache Iceberg version

main (development)

Please describe the bug 🐞

SqlCatalog currently uses exact match comparison (here and here) to find a namespace. However, when a namespace contains sub-namespaces, it should perform a LIKE comparison to account for that.

JdbcCatalog Java reference:
https://github.com/apache/iceberg/blob/472ec6cbdcaa24773ef5c64c9444ae933805381d/core/src/main/java/org/apache/iceberg/jdbc/JdbcUtil.java#L792

Willingness to contribute

• I can contribute a fix for this bug independently
• I would be willing to contribute a fix for this bug with guidance from the Iceberg community
• I cannot contribute a fix for this bug at this time