[#11841] fix ClickHouse partition expression round trip

[hutiefang76]

What changes were proposed in this pull request?

Fix ClickHouse partition expression round-tripping for day transforms and nested date wrappers:

• format Gravitino day transforms as toYYYYMMDD(column) instead of toDate(column)
• parse toYYYYMMDD(column) back to a day transform
• unwrap a supported toDate(...) wrapper when parsing expressions such as toYYYYMM(toDate(event_time))
• update the ClickHouse catalog documentation for supported partition functions

Why are the changes needed?

Fixes #11841.

Without this change, a ClickHouse partition expression like toYYYYMM(toDate(event_time)) is parsed with toDate(event_time) as the field name. Also, day transforms are formatted as toDate(...), which does not round-trip cleanly with the ClickHouse day partition form described in the issue.

Does this PR introduce any user-facing change?

Yes. ClickHouse day partition transforms are now generated as toYYYYMMDD(column). Existing toDate(column) partition expressions are still accepted when reading metadata.

How was this patch tested?

• JAVA_HOME=$(/usr/libexec/java_home -v 17) ./gradlew :catalogs-contrib:catalog-jdbc-clickhouse:test --tests org.apache.gravitino.catalog.clickhouse.operations.TestClickHouseTableOperationsPartitioning -PskipITs
• JAVA_HOME=$(/usr/libexec/java_home -v 17) ./gradlew :catalogs-contrib:catalog-jdbc-clickhouse:spotlessCheck -PskipITs
• git diff --check