feat(backend): state persisted objects (#9870)

This PR initiates the rework of Zitadel's backend to state-persisted
objects. This change is a step towards a more scalable and maintainable
architecture.

## Changes

* **New `/backend/v3` package**: A new package structure has been
introduced to house the reworked backend logic. This includes:
* `domain`: Contains the core business logic, commands, and repository
interfaces.
* `storage`: Implements the repository interfaces for database
interactions with new transactional tables.
  * `telemetry`: Provides logging and tracing capabilities.
* **Transactional Tables**: New database tables have been defined for
`instances`, `instance_domains`, `organizations`, and `org_domains`.
* **Projections**: New projections have been created to populate the new
relational tables from the existing event store, ensuring data
consistency during the migration.
* **Repositories**: New repositories provide an abstraction layer for
accessing and manipulating the data in the new tables.
* **Setup**: A new setup step for `TransactionalTables` has been added
to manage the database migrations for the new tables.

This PR lays the foundation for future work to fully transition to
state-persisted objects for these components, which will improve
performance and simplify data access patterns.

This PR initiates the rework of ZITADEL's backend to state-persisted
objects. This is a foundational step towards a new architecture that
will improve performance and maintainability.

The following objects are migrated from event-sourced aggregates to
state-persisted objects:

* Instances
  * incl. Domains
* Orgs
  * incl. Domains

The structure of the new backend implementation follows the software
architecture defined in this [wiki
page](https://github.com/zitadel/zitadel/wiki/Software-Architecturel).

This PR includes:

* The initial implementation of the new transactional repositories for
the objects listed above.
* Projections to populate the new relational tables from the existing
event store.
* Adjustments to the build and test process to accommodate the new
backend structure.

This is a work in progress and further changes will be made to complete
the migration.

---------

Co-authored-by: Copilot <[email protected]>
Co-authored-by: Iraq Jaber <[email protected]>
Co-authored-by: Iraq <[email protected]>
Co-authored-by: Tim Möhlmann <[email protected]>

backend/v3/storage/database/dialect/sql/tx.go

@@ -0,0 +1,104 @@
+package sql
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+
+	"github.com/zitadel/zitadel/backend/v3/storage/database"
+)
+
+type sqlTx struct{ *sql.Tx }
+
+var _ database.Transaction = (*sqlTx)(nil)
+
+func SQLTx(tx *sql.Tx) *sqlTx {
+	return &sqlTx{
+		Tx: tx,
+	}
+}
+
+// Commit implements [database.Transaction].
+func (tx *sqlTx) Commit(ctx context.Context) error {
+	return wrapError(tx.Tx.Commit())
+}
+
+// Rollback implements [database.Transaction].
+func (tx *sqlTx) Rollback(ctx context.Context) error {
+	return wrapError(tx.Tx.Rollback())
+}
+
+// End implements [database.Transaction].
+func (tx *sqlTx) End(ctx context.Context, err error) error {
+	if err != nil {
+		rollbackErr := tx.Rollback(ctx)
+		if rollbackErr != nil {
+			err = errors.Join(err, rollbackErr)
+		}
+		return err
+	}
+	return tx.Commit(ctx)
+}
+
+// Query implements [database.Transaction].
+// Subtle: this method shadows the method (Tx).Query of pgxTx.Tx.
+func (tx *sqlTx) Query(ctx context.Context, sql string, args ...any) (database.Rows, error) {
+	//nolint:rowserrcheck // Rows.Close is called by the caller
+	rows, err := tx.QueryContext(ctx, sql, args...)
+	if err != nil {
+		return nil, wrapError(err)
+	}
+	return &Rows{rows}, nil
+}
+
+// QueryRow implements [database.Transaction].
+// Subtle: this method shadows the method (Tx).QueryRow of pgxTx.Tx.
+func (tx *sqlTx) QueryRow(ctx context.Context, sql string, args ...any) database.Row {
+	return &Row{tx.QueryRowContext(ctx, sql, args...)}
+}
+
+// Exec implements [database.Transaction].
+// Subtle: this method shadows the method (Pool).Exec of pgxPool.Pool.
+func (tx *sqlTx) Exec(ctx context.Context, sql string, args ...any) (int64, error) {
+	res, err := tx.ExecContext(ctx, sql, args...)
+	if err != nil {
+		return 0, wrapError(err)
+	}
+	return res.RowsAffected()
+}
+
+// Begin implements [database.Transaction].
+// As postgres does not support nested transactions we use savepoints to emulate them.
+func (tx *sqlTx) Begin(ctx context.Context) (database.Transaction, error) {
+	_, err := tx.ExecContext(ctx, createSavepoint)
+	if err != nil {
+		return nil, wrapError(err)
+	}
+	return &sqlSavepoint{tx}, nil
+}
+
+func transactionOptionsToSQL(opts *database.TransactionOptions) *sql.TxOptions {
+	if opts == nil {
+		return nil
+	}
+
+	return &sql.TxOptions{
+		Isolation: isolationToSQL(opts.IsolationLevel),
+		ReadOnly:  accessModeToSQL(opts.AccessMode),
+	}
+}
+
+func isolationToSQL(isolation database.IsolationLevel) sql.IsolationLevel {
+	switch isolation {
+	case database.IsolationLevelSerializable:
+		return sql.LevelSerializable
+	case database.IsolationLevelReadCommitted:
+		return sql.LevelReadCommitted
+	default:
+		return sql.LevelSerializable
+	}
+}
+
+func accessModeToSQL(accessMode database.AccessMode) bool {
+	return accessMode == database.AccessModeReadOnly
+}