Fix issues with openapi spec

[tylerjmchugh]

Some API endpoints currently use HttpStatus as their response body type even though they do not return a response body. This causes OpenAPI to interpret HttpStatus as response content and generate an enum schema containing the possible status values.

The harvester reindex endpoint is also currently documented with both 200 and 204 success responses, even though it returns 204.

In addition, the DOI server and mapserver delete endpoints currently have conflicting generated operation IDs. This causes the generated _1 suffix to switch between the endpoints depending on their order in the OpenAPI specification, resulting in unstable generated client method names.

This PR aims to fix these issues by:

• Replacing ResponseEntity<HttpStatus> and HttpEntity<HttpStatus> with ResponseEntity<Void> for endpoints that do not return a response body. The response status continues to be set through the ResponseEntity, while Void correctly indicates to OpenAPI that the response does not contain content.
• Removing @ResponseStatus(HttpStatus.OK) from the harvester reindex endpoint so that 204 is the only documented success response.
• Adding explicit deleteDoiServer and deleteMapserver operation IDs to prevent conflicts and keep the generated method names stable.

Checklist

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