Fix type of purl fields in Swagger docs

[sebD]

Description

Adds a custom deserializer for pURL properties of Project and Component objects. This deserializer allows to describe pURL either as text value or object value in JSON payloads to better conform to the swagger api definitions.

Addressed Issue

Fixes: #3509

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

[nscuro]

Thanks for the PR @sebD. However, I don't believe we should fix the issue this way, see #3509 (comment).

Are you happy to revise this PR to apply the suggested change instead? Otherwise please let me know, and I'll raise a separate PR.

[codacy-production]

Coverage summary from Codacy

See diff coverage on Codacy

Coverage variation	Diff coverage
✅ +0.00% (target: -1.00%)	✅ ∅ (target: 70.00%)

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (8b23434)	21360	15775	73.85%
Head commit (54df0dd)	21360 (+0)	15775 (+0)	73.85% (+0.00%)

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 (#3512)	0	0	∅ (not applicable)

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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[nscuro]

Thanks!