Do not hide diagnostics in RepositoryValidatingInterceptor

[MartinBernstorff]

Currently, the RepositoryValidatingInterceptor outputs only the first issue, whether or not that is the issue that triggers the operation to fail validation. E.g. if the first issue is INFO, the user will not be informed why the validation failed.

This is a simple improvement that outputs diagnostics for all issues. This does change default behaviour, so we could feature-flag it.

Ideally, I think we'd:

• Sort the issues by severity
• Output SEVERITY: Diagnostics

But I am not certain whether this information is available from the IBaseOperationOutcome, because the code in OperationOutcomeUtil.getIssueStringPart is quite reflexive :-)

Tests

• Tried unit testing by parsing JSON from a real example. However, we cannot initialise a FhirContext in hapi-fhir-base, because it does not include any FHIR structure JARs.
• I ended up with static mocking instead. Note that all new code in OperationOutcomeUtil is covered by the test.

[jamesagnew]

This is a good idea. Would you mind to add a test of the new behaviour? Presumably RepositoryValidatingInterceptorR4Test would be a good place for it.