Bug Report: Switch from `tx_isolation ` to `transaction_isolation`

[corbantek]

Overview of the Issue

MySQL 8.0 has deprecated the use of tx_isolation variable in favor of the backwards compatible (up to 5.7.20) transaction_isolation

References:

• https://dev.mysql.com/doc/refman/8.0/en/server-options.html#option_mysqld_transaction-isolation
• https://dev.mysql.com/doc/refman/5.7/en/server-options.html#option_mysqld_transaction-isolation
• https://dev.mysql.com/doc/refman/5.7/en/server-system-variables.html#sysvar_tx_isolation

For the Java JDBC src in Vitess, we should switch to using transaction_isolation instead of tx_isolation

Reproduction Steps

Using the Java Client to create a VitessConnection results in the transaction isolation being blank...

Binary Version

N/A

Operating System and Environment details

MYSQL_VERSION=8.0.33

`uname -sr` 

Linux 6.1.109-hs83.el9.x86_64

Log Fragments

[corbantek]

FYI: PR in-flight