SO-6081: support multiple FHIR versions in the REST API

[cmark]

This PR adds support for multiple FHIR mime types, supporting R4, R4B, and R5.
This PR also adds a new operation CapabilityStatement$versions to list the available versions in Snow Owl.

[nagyo]

LGTM so far!

[apeteri]

👍

[codecov]

Codecov Report

Attention: Patch coverage is 42.85714% with 160 lines in your changes missing coverage. Please review.

Project coverage is 63.63%. Comparing base (8e1a9ea) to head (2a09f67).
Report is 15 commits behind head on 9.x.

Files with missing lines	Patch %	Lines
...international/snowowl/fhir/rest/FhirMediaType.java	44.56%	91 Missing and 11 partials ⚠️
...onal/snowowl/fhir/rest/AbstractFhirController.java	48.64%	18 Missing and 1 partial ⚠️
...ir/rest/FhirValueSetExpandOperationController.java	12.50%	2 Missing and 12 partials ⚠️
...wl/fhir/rest/FhirCodeSystemSubsumesController.java	14.28%	6 Missing ⚠️
...l/fhir/rest/FhirConceptMapTranslateController.java	0.00%	6 Missing ⚠️
.../fhir/rest/FhirValueSetValidateCodeController.java	0.00%	6 Missing ⚠️
...owl/fhir/rest/FhirVersionsOperationController.java	14.28%	6 Missing ⚠️
...hir/rest/FhirCodeSystemValidateCodeController.java	75.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##                9.x    #1332      +/-   ##
============================================
- Coverage     63.68%   63.63%   -0.06%     
- Complexity    12471    12486      +15     
============================================
  Files          1609     1611       +2     
  Lines         56809    56955     +146     
  Branches       5595     5598       +3     
============================================
+ Hits          36180    36244      +64     
- Misses        18295    18375      +80     
- Partials       2334     2336       +2     

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[apeteri]

🍃