Cleanup GHES Archives

When migrating from GHES we ask GHES to generate migration archives which we then download and upload to Azure. However, we don't explicitly tell GHES to delete the archives when we're done with them, which can potentially cause disk space issues on the GHES server.

I believe GHES will automatically clean them up after 7 days, however we could have the CLI call the appropriate API's to clean them up as soon as we are done with them (i.e. after we download them).