Clean up state management for user management page

[rtibbles]

Summary

• Removes loading state when moving between pages of the user management page
• Set default state to ensure reactivity from Object.assign.

References

Fixes #9528

Reviewer guidance

Does the user management page in Facility still function as expected - for filtering, pagination? Does it show the correct number of users once filtering has happened or been removed?

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Testing checklist

• Contributor has fully tested the PR manually
• If there are any front-end changes, before/after screenshots are included
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• Critical and brittle code paths are covered by unit tests

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Reviewer checklist

• Automated test coverage is satisfactory
• PR is fully functional
• PR has been tested for accessibility regressions
• External dependency files were updated if necessary (yarn and pip)
• Documentation is updated
• Contributor is in AUTHORS.md

[marcellamaki]

Welp, I approved this with just a code review, but it actually looks like there's an error when I run it...so, I take that back. The filtering and searching itself seems fine, just the pagination numbers and buttons are the issue seems like

Although, I can't quite figure out how this is exactly related to these changes

[marcellamaki]

I checked out 0.15.x because I briefly panicked that I had broken this during our patch release speeding along, but it seems to be working there

[marcellamaki]

Can not replicate again -- seems to be due to branch switch or some such. Approved!