Updated to newer openapi-generator-cli

[nils-work]

Added new jar and removed/replaced older jars.
Addresses #414

[markverstege]

Not approved until we review the Swagger file outputs and understand API contract impacts.

[nils-work]

The newer version of the openapi-generator-cli (openapi-generator-cli-6.6.0.jar) provides recommendations in relation to the validity of the spec files that were not provided by the version used in previous builds.

Examples from build logs with previous version stating No validation issues detected:

*** Input Swagger:  api/cds_dcr.json
*** Output Format:  openapi
*** Output Extension json
*** Output Dir: ../slate/source/includes/swagger
*** Checking OAS Validator ***
 No validation issues detected.spec (api/cds_dcr.json)

*** Input Swagger:  api/cds_telco.json
*** Output Format:  openapi
*** Output Extension json
*** Output Dir: ../slate/source/includes/swagger
*** Checking OAS Validator ***
 No validation issues detected.spec (api/cds_telco.json)

Examples from build logs with updated version stating [info] Spec has ... recommendation(s):

*** Input Swagger:  api/cds_dcr.json
*** Output Format:  openapi
*** Output Extension json
*** Output Dir: ../slate/source/includes/swagger
*** Checking OAS Validator ***
 [info] Spec has 1 recommendation(s).api/cds_dcr.json)

In the DCR spec., this recommendation appears to relate to the ClientRegistration definition being declared but not used (not directly referenced by an endpoint).

*** Input Swagger:  api/cds_telco.json
*** Output Format:  openapi
*** Output Extension json
*** Output Dir: ../slate/source/includes/swagger
*** Checking OAS Validator ***
 [info] Spec has 7 recommendation(s).tResponseontactson)

In the Telco spec., these recommendations appear to refer to unused definitions:

• TelcoServiceUsageListResponse
• TelcoServiceDetail
• CommonPhysicalAddress
• TelcoAccountDetailAuthorisedContacts

Validation of the OpenAPI spec. files early in the testing and build process helps to avoid redundant detail and errors at the final build stage.