Don't reveal private project exists to anonymous user

[harminius]

fixes https://github.com/MerginMaps/server-private/issues/3087#issuecomment-3586086194

return 404 to anonymous user requesting private project info
a new flag ensures it is applied only in specific endpoints -> does not affect other responses but v2 get project info

add validation for version in API spec

[coveralls]

Pull Request Test Coverage Report for Build 19921201757

Details

• 36 of 45 (80.0%) changed or added relevant lines in 4 files are covered.
• 87 unchanged lines in 6 files lost coverage.
• Overall coverage decreased (-0.01%) to 94.339%

---

Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
server/mergin/tests/test_middleware.py	25	34	73.53%

Files with Coverage Reduction	New Missed Lines	%
server/mergin/tests/test_public_api_v2.py	1	99.62%
server/mergin/tests/test_utils.py	1	98.94%
server/mergin/sync/tasks.py	7	90.11%
server/mergin/sync/public_api_v2_controller.py	14	90.61%
server/mergin/sync/utils.py	18	84.85%
server/mergin/sync/public_api_controller.py	46	92.14%

Totals
Change from base Build 19667930641:	-0.01%
Covered Lines:	7982
Relevant Lines:	8461

---

💛 - Coveralls

[MarcelGeo]

Just fix a test and it's fine :)