[local] Parse Task Definition as yaml for up/create

[SoManyHs]

Currently, local subcommands take Task definitions files as JSON. We would also like to support YML files.

Related: https://github.com/aws/amazon-ecs-cli/issues/825

Summary

Description

• Which specific command was run? (Example: ecs-cli up --capability-iam --size 2 --launch-type EC2)
• Which version of the CLI you are using? (Run: ecs-cli --version)
• Which version of Go are you using? (Run: go version)
• What platform are you using to run ECS CLI commands? (E.g. Linux, MacOSX, Windows)

Config files

• docker-compose.yml

• ecs-params.yml

• ~/.ecs/config

Expected Behavior

Observed Behavior