use_allof_for_refs: extend to example field

[igor-tsiglyar]

References to other Issues or PRs

Related to #3232, #2671

Have you read the Contributing Guidelines?

Yes

Brief description of what is fixed or changed

Extending #3082, we can enable setting enum field example in openapiv2_field annotation, e.g.

  // Severity of this alert
  AlertSeverity severity = 5 [
    (grpc.gateway.protoc_gen_openapiv2.options.openapiv2_field) = {
      example: "\"CRITICAL\""
    }
  ];

produces

        "severity": {
          "example": "CRITICAL",
          "title": "Severity of this alert",
          "allOf": [
            {
              "$ref": "#/definitions/AlertSeverity"
            }
          ]
        },

instead of example field being ignored, which is currently the case.

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[johanbrandhorst]

This seems reasonable, but I think we should add at least one test. Either add a new test case in template_test.go (there's hopefully already one for the allOf option) or add a new protobuf file and generate from it with this option enabled please.

[igor-tsiglyar]

@johanbrandhorst I have extended the existing relevant test to verify the example property being included, as well as others from the include condition (title, description) https://github.com/grpc-ecosystem/grpc-gateway/pull/3240/files#diff-0330d83e3109c5c0a8cb78a2a980db731e973c738da7851d34a88e00244a4b5eR5375

[johanbrandhorst]

LGTM

[johanbrandhorst]

Thanks for your contribution!

[igor-tsiglyar]

@johanbrandhorst Sure, thanks for driving this project