Add a new option: use_tls

[loic-vial]

Hello !

Thank you for the work done on this plugin ! I am currently using it for accessing JupyterHub in our data science team at my company, but I needed to add an option "use_tls" and set it to False to actually make it work. That is because we need to connect to a LDAP server that needs this configuration.

For information, such option exists in the LDAP connector used by Airflow, another tool that we are also using. There is distincts "USE_SSL" and "USE_TLS" options for addressing our use case, so I just applied the same logic.

I hope that my PR is correct, I simply added the option "use_tls" and a small test for testing the option. I also needed to update the black pre-commit hook because it didn't work on my computer.

Obviously, the default value of this option does not change anything on the current behavior.

Thank you !

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