[OAS 3.1.0] Add identifier to License

[jmini]

In order to support OpenAPI 3.1.0 (see #333) we need to add identifier to the License object.

Reference: https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.1.0.md#licenseObject

An SPDX license expression for the API. The identifier field is mutually exclusive of the url field.

Example:

openapi: 3.1.0
info:
  title: Example specification
  version: "1.0"
  license:
    name: Eclipse Public License 2.0
    identifier: EPL-2.0
servers:
- url: http://localhost:8080/
paths:
  /ping:
    get:
      operationId: ping
      responses:
        200:
          description: OK

To be added:

• The model interface License.java: new methods (getter, setter, builder)
• The annotation definition License.java: new method
• TCK tests

As previously discussed (#339 or #331), it is not the role of the MicroProfile OpenAPI to add checks to ensure that identifier and url can not be set simultaneously. This is up to the vendor.

[benjamin-confino]

Please assign this one to me