fix: keep cors config on project update

[jonas-jonas]

Fixes a bug, where the project's CORS configuration was lost if either of the oauth2-config, identity-config or permissions-config was updated individually.

Related Issue or Design Document

Checklist

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• I have referenced an issue containing the design document if my change
  introduces a new feature.
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Further comments

[zepatrik]

Should we maybe use the patch API instead and handle this server-side?

[jonas-jonas]

Yea, but that endpoint works differently, and I really don't want to find out what bugs that would uncover... Let's just merge this, and keep an item in the backlog to refactor this. WDYT?