Unable to compare DATETIME and TIMESTAMP[BUG]

[ghost]

Describe the bug
Unable to compare DATETIME and TIMESTAMP for logical operators and CASE.

Or for query issues:'

1. Run the query 'SELECT TIMESTAMP(DATE("2010-04-12")) = SUBDATE(TIMESTAMP(DATE("2010-04-12")), INTERVAL 1 HOUR)'
2. See error "ExpressionEvaluationException"

Expected behavior
The SQL plugin should be able to compare DATETIME and TIMESTAMP or SUBDATE and ADDDATE should have output of type TIMESTAMP.

Screenshots

[dai-chen]

The root cause seems implicit conversion between DATETIME and TIMESTAMP is not supported. Code: https://github.com/opensearch-project/sql/blob/main/core/src/main/java/org/opensearch/sql/data/type/ExprCoreType.java#L58