OpenScenario encoder

[hcn1519]

• [x] Support encoding object which generates yaml format scenario files
  • [x] It should remove oneof type object from the tree.
  • [x] Change field name to type name
  • Values
    • [x] enum, unsupported value conversion
    • [x] #26
• [x] #27

[hcn1519]

https://tier4.github.io/scenario_simulator_v2-docs/user_guide/scenario_test_runner/Tips/