refactor: unify db dialect definition in dbdialects package

internal/app/db-wrapper/db-dialects/main.go

@@ -0,0 +1,7 @@
+package dbdialects
+
+const (
+	SqlServer string = "sqlserver"
+	Postgres  string = "postgres"
+	Null      string = "null"
+)

internal/app/db-wrapper/mssql.go

@@ -5,12 +5,13 @@ import (
 	"database/sql"
 	"fmt"
 
+	dbdialects "git.ksdemosapps.com/kylesoda/go-migrate/internal/app/db-wrapper/db-dialects"
 	mssql "github.com/microsoft/go-mssqldb"
 )
 
 func init() {
-	Register("sqlserver", func() DbWrapper {
+	Register(dbdialects.SqlServer, func() DbWrapper {
-		return &mssqlDbWrapper{dialect: "sqlserver"}
+		return &mssqlDbWrapper{dialect: dbdialects.SqlServer}
 	})
 }
 

internal/app/db-wrapper/postgres.go

@@ -4,13 +4,14 @@ import (
 	"context"
 	"errors"
 
+	dbdialects "git.ksdemosapps.com/kylesoda/go-migrate/internal/app/db-wrapper/db-dialects"
 	"github.com/jackc/pgx/v5"
 	"github.com/jackc/pgx/v5/pgxpool"
 )
 
 func init() {
-	Register("postgres", func() DbWrapper {
+	Register(dbdialects.Postgres, func() DbWrapper {
-		return &postgresDbWrapper{dialect: "postgres"}
+		return &postgresDbWrapper{dialect: dbdialects.Postgres}
 	})
 }