Ensure no unique constraint violation for ProjectMetadata

[nscuro]

Description

Adds regression test for #3895. The behavior itself does not reproduce on master, but does with 4.11.5.

Wraps the project cloning in a transaction to make it more reliable. Adds MDC variables for CloneProjectTask (#3234).

Addressed Issue

Fixes #3895
Relates to #3981

Additional Details

N/A

Checklist

• I have read and understand the contributing guidelines
• This PR fixes a defect, and I have provided tests to verify that the fix is effective
• This PR implements an enhancement, and I have provided tests to verify that it works as intended
• This PR introduces changes to the database model, and I have added corresponding update logic
• This PR introduces new or alters existing behavior, and I have updated the documentation accordingly

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.04% (target: -1.00%)	✅ 91.13% (target: 70.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (84eca3c)	22097	16869	76.34%
Head commit (164847a)	22108 (+11)	16887 (+18)	76.38% (+0.04%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#3982)	124	113	91.13%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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