Don't allow SSO users update their profile

[harminius]

Users that signed in with SSO are not allowed to change their email, name or password.

Frontend does not show the button to update the profile. 🪹

Backend blocks profile update ⛔

Unittest only for admin endpoint as I'm not able to login as SSO user (right now)

[coveralls]

Pull Request Test Coverage Report for Build 14213913227

Details

• 31 of 31 (100.0%) changed or added relevant lines in 5 files are covered.
• 14 unchanged lines in 2 files lost coverage.
• Overall coverage decreased (-0.04%) to 92.274%

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Files with Coverage Reduction	New Missed Lines	%
server/mergin/auth/app.py	1	98.63%
server/mergin/auth/controller.py	13	91.93%

Totals
Change from base Build 14167313338:	-0.04%
Covered Lines:	6891
Relevant Lines:	7468

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💛 - Coveralls