Add json output format

[ibizaman]

Thank you for this tool! I've been following it since you announced it in the PR in the lldap project.

I am working on integrating lldap-cli into NixOS. As you may know, NixOS is all about declarative setup, so I'm creating a script which runs lldap-cli command according to some static config to create/delete groups and users and memberships to groups.

The current output format of lldap-cli is made for users, with its tab separated format. For what I'm doing, this is really hard to parse. Instead, keeping the original json format coming out of graphql is much more valuable in this case. Would you be okay to add an option to change the output format to json?

I created a fork which simply changes the output format from tsv to json, without giving an option to choose. ibizaman@e07e2ca I won't create a PR with this but it gives an idea of the amount of work this will entail.
Btw, I'd be happy to create a proper PR but I'd like some guidance on how to integrate handling such an option in the script.