v6.0.0

• Allow adding multiple values with same key in BUILD_EXTRA_ARGS. (Close #95)
• Avoid action to stop prematurely at getting context for build. (Close #98)
• Fix AWS public repositories support. (Close #104)
• Use dummy tag instead of dummy image name to avoid confusion in the logs. (Close #106)
• Get AWS_SESSION_TOKEN from the env if INPUT_SESSION is not set. (Close #108)
• Use yaml parser to allow comments in compose-file and improve code overall. (Close #111)
• Stop using deprecated set-output command. (Close #113)
• Create ECR repository only if we need to push images.