Description

We can expand the pipeline conversion to support piping from standard in;

cat ci.yml | bk pipeline convert --vendor github

Changes

• allows users to pipe to the CLI via tools like cat using our HasDataAvailable method
• makes --file optional due to stdin support
• pipes back to stdout (unless --output/-o specified)

Testing

• Tests have run locally (with go test ./...)
• Code is formatted (with go fmt ./...)