Support configurable MultiStatementEnabled for PostgreSQL migrations

[ClaraTersi]

Problem

The PostgresConnection.Connect() method has MultiStatementEnabled: true hardcoded when creating the
golang-migrate driver:

primaryDriver, err := postgres.WithInstance(dbPrimary, &postgres.Config{
    MultiStatementEnabled: true,  // hardcoded
    DatabaseName:          pc.PrimaryDBName,
    SchemaName:            "public",
})

This prevents consumers from controlling whether migrations run with multi-statement mode enabled or disabled.

Proposal

Add a MultiStatementEnabled *bool field to PostgresConnection struct:

type PostgresConnection struct {
    // ... existing fields ...
    MultiStatementEnabled *bool  // nil = default true (backward compatible)
}

Update Connect() to use the field with default true:

multiStmtEnabled := true
if pc.MultiStatementEnabled != nil {
    multiStmtEnabled = *pc.MultiStatementEnabled
}

Usage example

type Config struct {
    // ... other fields ...

    // PostgreSQL migration settings
    MultiStatementEnabled *bool `env:"DB_MULTI_STATEMENT_ENABLED"`
}

postgresConnection := &libPostgres.PostgresConnection{
    ConnectionStringPrimary: connStr,
    // ... other fields ...
    MultiStatementEnabled:   cfg.MultiStatementEnabled,  // nil = defaults to true
}

Why pointer?

Using *bool instead of bool allows distinguishing between:

• nil → not configured, use default true
• &true → explicitly enabled
• &false → explicitly disabled

Backward Compatibility

• Default behavior unchanged (true)
• No breaking changes to existing consumers
• Field is optional