feat: Possibility to set if the transaction is read only or not

[Crovitche-1623]

Feature Request

What

On many RDBMS, it's possible to specify if the transaction is read only or not (READ WRITE). By default, a transaction is READ WRITE. When a transaction is set to READ ONLY, it prevent any modification during the transaction and can improve performance in certain cases.

Moreover, I think this READ ONLY / READ WRITE flag is supported by most platforms:

• Oracle: https://docs.oracle.com/en/database/oracle/oracle-database/23/sqlrf/SET-TRANSACTION.html
• PostgreSQL: https://www.postgresql.org/docs/current/sql-set-transaction.html
• MySQL: https://dev.mysql.com/doc/refman/8.4/en/set-transaction.html
• MariaDB: https://mariadb.com/kb/en/set-transaction/
• IBM DB2: https://www.ibm.com/docs/en/i/7.4?topic=statements-set-transaction

Why

1. It can improve performance in certain circumstances. E.g. when SERIALIZABLE TRANSACTIONS are used. See https://www.postgresql.org/docs/current/transaction-iso.html
2. It can improve security in some ways by specifying that no modifications are expected during the transaction.

How

Maybe add a readOnly parameter to the getSetTransactionIsolationSQLmethod with false as the default value:

abstract public function getSetTransactionIsolationSQL(TransactionIsolationLevel $level, bool $readOnly = false): string;

and use this value later to conditionally add READ WRITE or READ ONLY to the statement.