Add new v2 push endpoint to create a project version

[varmar05]

• refactor common logic for push in v1 and v2 API
• feature flag to use v2 push (for clients only)
• dry run option in v2 endpoint to only validate request
• use new error structure for v2 endpoint

[coveralls]

Pull Request Test Coverage Report for Build 16771522870

Details

• 483 of 526 (91.83%) changed or added relevant lines in 17 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 91.863%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
server/mergin/sync/commands.py	0	1	0.0%
server/mergin/sync/public_api_controller.py	65	66	98.48%
server/mergin/tests/test_public_api_v2.py	94	95	98.95%
server/mergin/sync/errors.py	34	38	89.47%
server/mergin/sync/files.py	67	71	94.37%
server/mergin/sync/models.py	84	92	91.3%
server/mergin/sync/public_api_v2_controller.py	86	110	78.18%

Files with Coverage Reduction	New Missed Lines	%
server/mergin/sync/utils.py	2	84.54%

Totals
Change from base Build 16745450194:	-0.1%
Covered Lines:	7417
Relevant Lines:	8074

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💛 - Coveralls

[MarcelGeo]

just questions.