Support `gh gei migrate-repo` with archives stored in the local machine (`--git-archive-path`, `--metadata-archive-path`)

When you run `gh gei migrate-repo`, the migration runs end-to-end, exporting data from your source GitHub instance and importing it into your destination GitHub instance.

In some scenarios, you may already have the Git archive and metadata archive on your local machine, and want to import it.

This is supported - but you have to upload the file to a blob storage provider yourself, generate a URL for the file and then call `migrate-repo` with the `--git-archive-url` and `--metadata-archive-url` arguments.

The process of importing an already-existing archive would be easier if you could pass a `--git-archive-path` and `--metadata-archive-path` instead, and ask the CLI to upload it to blob storage for you and generate a URL.