Move SAML group filtering to GroupsFinder
What does this MR do and why?
The SAML group filtering logic is not specific to Organizations::GroupsFinder so it is moved to GroupsFinder.
A request spec is also added for organization groups to avoid a regression.
This also aligns with Fix GraphQL query returning less than expected ... (!160592 - merged).
MR acceptance checklist
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Query plan
The query hasn't changed here. If you want to see the query plans see Query plans.
How to set up and validate locally
See How to set up and validate locally
Related to #461083