Add wildcard (*) support to GetMigrations, ScriptMigration, and DropDatabase

[BrunoSync]

Implements wildcard (*) support for contextType in three methods of MigrationsOperations, following the same pattern established in the previous wildcard implementation.

Changes:

• GetMigrations: iterates all contexts and aggregates MigrationInfo results
• ScriptMigration: iterates all contexts and concatenates generated scripts
• DropDatabase: iterates all contexts and drops each database

Not implemented:

• RemoveMigration: wildcard not applicable — the command only supports unapplied migrations, making a wildcard operation semantically ambiguous
• GetContextInfo: current signature returns a single ContextInfo object. Supporting wildcard would require changing the return type to IEnumerable, which is a breaking change. Happy to implement if the team decides on the preferred approach. Same for AddMigrations.

Tested manually.