Fix swagger, make login_name snake case

[TatevikGr]

Summary

Fix swagger response
Use core with configured normalizer (snake case fix)

Unit test

Are your changes covered with unit tests, and do they not break anything?

You can run the existing unit tests using this command:

vendor/bin/phpunit tests/

Code style

Have you checked that you code is well-documented and follows the PSR-2 coding
style?

You can check for this using this command:

vendor/bin/phpcs --standard=PSR2 src/ tests/

Other Information

If there's anything else that's important and relevant to your pull
request, mention that information here. This could include benchmarks,
or other information.

If you are updating any of the CHANGELOG files or are asked to update the
CHANGELOG files by reviewers, please add the CHANGELOG entry at the top of the file.

Thanks for contributing to phpList!