Improved metrics

[Adaickalavan]

• Made the metrics module configurable by supplying parameters through a Params class.
• Params allows to specify vehicles to be ignored in dist_to_obstacles cost function. This would be applicable in platooning tasks.
• Unified computation of dist_to_destination (previously known as completion) and steps (i.e., time taken) as functions inside the cost functions module, instead of computing them separately in a different module.
• In the metrics module, the records which is the raw metrics data and the scoring which is the formula to compute the final results are now separated to provided greater flexibility for applying metrics to different environments.
• Changed benchmark_runner_v0.py to only average records across scenarios within an environment. Records are not averaged across enviroments, because the scoring formula may differ in different environments.
• Fixed CI tests for metrics.