fixed issue #5517: H2 database field type error causing 'Value too long for column' exception

- Changed meta_snapshot.data from longtext to CLOB in H2 schema
- Changed meta_history.sql_text from longtext to CLOB in H2 schema
- H2 database doesn't recognize MySQL's longtext type and converts it to VARCHAR with length limit
- CLOB type supports up to 2GB text data, solving the issue when storing large table structures (>1MB DDL)