Handle init shell logs being sent to IoHost

Data chunks from [the init workflow's shell process](https://github.com/aws/aws-cdk/blob/173a204c5856586e7350f89dd0d254892f239e18/packages/aws-cdk/lib/os.ts#L26) today are written directly to stdout. These could be strings or Buffers and the IoHost should be able to explicitly be able to handle these data chunks 

https://github.com/aws/aws-cdk/pull/32708#discussion_r1913777530