feature: Domain Join use SSSD instead of winbindd

I've been evaluating using the seamless domain join with Linux EC2 instances and noticed that it currently relies on winbindd and Samba rather than using SSSD. I would rather use SSSD but haven't seen anyway of doing so short of giving up on the existing seamless domain join functionality and handling it manually.

Any thoughts on making this a supported feature? Both can be done via the `realm` command just changing the `--client-software` option passed to realm when joining the domain. I believe most modern available Linux distributions all have SSSD available,

Start by tracing the seamless domain join flow to the realm command and compare how its --client-software option selects winbindd versus SSSD. Review the existing join behavior and discussion, then define support that preserves the current path while allowing SSSD on supported Linux distributions; done means both client options work through seamless domain join.

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