issue 3751 use client-configuration endpoint on FES

[tomholub]

This PR uses this endpoint https://fes.flowcrypt.com/api/v1/client-configuration?domain=flowcrypt.com (or similar depending on customer domain) to fetch client configuration (org rules) from FES, instead of the /api/v1/account/ endpoint which was authenticated.

This is to avoid relying on a non-OIDC access token, which our customer doesn't prefer.

close#3751

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Tests(delete all except exactly one):

• Tests updated

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To be filled by reviewers

I have reviewed that this PR... (tick whichever items you personally focused on during this review):

• addresses the issue it closes (if any)
• code is readable and understandable
• is accompanied with tests, or tests are not needed
• is free of vulnerabilities
• is documented clearly and usefully, or doesn't need documentation

[tomholub]

I'll self-review this because it's due soon for a security penetration testing that was scheduled.