Fix: deletion of ProjectProperties

[BastiaanN]

Deletion of project properties currently fails with the following error message:

{
  "status": 400,
  "title": "The provided JSON payload could not be mapped",
  "detail": "Cannot coerce empty String (\"\") to `alpine.model.IConfigProperty$PropertyType` value (but could if coercion was enabled using `CoercionConfig`)\n at [Source: REDACTED (`StreamReadFeature.INCLUDE_SOURCE_IN_LOCATION` disabled); line: 1, column: 92] (through reference chain: org.dependencytrack.model.ProjectProperty[\"propertyType\"])"
}

This happens because the ProjectProperty struct includes all fields when marshalling to json, including empty fields. The DT api does not allow an empty propertyType.

I thought about adding omitempty to all fields except groupName and propertyName but that might break semantics of the other calls. Instead, i created a new ProjectPropertyDelete struct that only includes the two fields needed for the delete endpoint.

I also used AI (Claude Opus 4.6) to generate tests for projectProperties, which i reviewed and modified carefully and take full responsibility for. I also noted that the GetAll method accepts PageOptions but that the API is not paginated at all. As a result totalCount is always returned as 0. This PR does not fix that.

[owasp-dt-bot]

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[nscuro]

Thanks!