Accept tags for operations from parent contexts

[drewish]

RSpec.describe "Sample Requests", type: :request, tags: [:context_tag] do
  path '/posts', tags: ['path_tag'] do
    operation "GET", summary: "fetch list" do
      produces 'application/json'
      tags 'operation_tag'

      response(200, {description: "successful"})
    end
  end
end

Would produce:

{
  "swagger": "2.0",
  "info": {
    "title": "API V1",
    "version": "v1"
  },
  "paths": {
    "/posts": {
      "get": {
        "responses": {
          "200": {
            "description": "successful"
          }
        },
        "tags": [
          "context_tag",
          "path_tag",
          "operation_tag"
        ],
        "summary": "fetch list",
        "produces": [
          "application/json"
        ]
      }
    }
  }
}