fix: refactor migrations; avoid mysql2 bugs by removing charset/collation directives

[csmig]

Refactor the initial six migrations:

• wrap the migration code in try/catch blocks for reliability and to throw more specific error messages

Avoid invoking buggy behavior from the mysql2 library:

• remove character set and collation directives from SQL scripts, which avoids mysql2 incorrectly over-writing its pool configuration options with the incorrect collation utf8mb4_general_ci.
• explicitly set the collation of pool connections to utf8mb4_0900_ai_ci, in accodance with current MySQL 8.x defaults, to avoid mysql2 incorrectly defaulting to utf8mb4_unicode_ci.

Remove explicit charset/collation references from existing queries:

• ReviewService.js
• OperationService.js