[launch] allow cloud-init file injection

Some cloud-init modules (e.g. [scripts](https://cloudinit.readthedocs.io/en/latest/topics/modules.html#scripts-per-boot)) require files to be placed into the data source.

We need a `--cloud-init-files` or so that will allow the user to specify a file/directory tree to be included on the data source.

Start at the launch command and its cloud-init data-source handling. Trace how launch options reach the data source, then verify how cloud-init modules such as scripts-per-boot access injected files. Done means a --cloud-init-files-style option accepts a file or directory tree and includes it in the data source.

Written by the indexing model from the issue text.