Backport to branch(3) : WIth the JDBC transaction manager, use the storage default transaction isolation level instead of SERIALIZABLE

[feeblefakie]

This is an automated backport of the following:

• Original PR: WIth the JDBC transaction manager, use the storage default transaction isolation level instead of SERIALIZABLE #3076
• Backported commit: 7a2d999

Please merge this PR after all checks have passed.

[gemini-code-assist]

Summary of Changes

Hello @feeblefakie, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request is an automated backport that modifies the JDBC transaction manager's behavior regarding transaction isolation levels. Previously, it explicitly set the isolation level to SERIALIZABLE. This change removes that explicit setting, allowing the system to utilize the default isolation level provided by the underlying database storage. This can offer greater flexibility and potentially better performance depending on the specific database configuration and workload.

Highlights

• JDBC Transaction Isolation: The explicit setting of the default transaction isolation level to SERIALIZABLE for JDBC transaction managers has been removed.
• Default Isolation Level: The system will now rely on the underlying storage's default transaction isolation level instead of forcing SERIALIZABLE.

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[gemini-code-assist]

Code Review

This pull request backports a change that removes the hardcoded default transaction isolation level of SERIALIZABLE for JDBC transactions. Instead, it will now use the underlying storage's default isolation level unless one is explicitly specified in the configuration. This change improves flexibility and aligns with the expected behavior of using database defaults. The change itself is correct, but I've suggested adding a unit test to cover the new default behavior to prevent regressions.