fix(java-sdk): fix transactions mode being reversed

[jimmyjames]

Description

⚠️ This is a behavioral breaking change!

Currently the OpenFgaClient reverses the behavior of write transactions based on the disableTransactions flag. This PR fixes that, only sending batched write requests if disableTransactions == true.

This is a functional breaking change, since the value of disableTransactions was being used incorrectly, so now disableTransactions == true will actually batch requests, and disableTransactions == false will send one (transactional) request.

Current Behavior	disabledTransactions value	Behavior
true	One transactional request sent
false	Batched requests sent

Behavior with this PR	disabledTransactions value	Behavior
true	Batched requests sent
false	One transactional request sent

References

https://github.com/openfga/java-sdk/issues/59

Review Checklist

• [x] I have clicked on "allow edits by maintainers".
• [ ] I have added documentation for new/changed functionality in this PR or in a PR to openfga.dev [Provide a link to any relevant PRs in the references section above]
• [x] The correct base branch is being used, if not main
• [x] I have added tests to validate that the change in functionality is working as expected