feat: document Google SCIM

[niwsa]

Related Issue or Design Document

Checklist

• I have read the contributing guidelines and signed the CLA.
• I have referenced an issue containing the design document if my change introduces a new feature.
• I have read the security policy.
• I confirm that this pull request does not address a security vulnerability.
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• I have added tests that prove my fix is effective or that my feature works.
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Further comments

[vinckr]

nice! looks great already,
some minor style comments, but otherwise looks good to me.

I haven't tested this though.

One other thing to think about: there are quite a lot of screenshots in this doc - how can we make sure these are up to date? Ideally it would be automated, but in general it's an unsolved problem for the docs. Maybe @unatasha8 has an idea how we can keep screenshots up to date without much manual work.

otherwise looks good to me!

[vinckr]

lgtm