Add ability to do a dry run of installation

[markpundsack]

Add something like kots --install --dry-run, so that you can run through preflight and other checks to see any errors or warnings, or to see if success is likely, before committing to doing an install. This may only be useful for unattended "automated" installs, where license and config are included in the command line as well. Currently, this isn't really possible because automated installs install the admin console before processing preflights, which would mean that it's not really a full dry-run. It could be a dry-run of the app installation at least, but that's not quite the same thing. Might still be beneficial.

[markpundsack]

Running preflights before installing the admin console could be part of the solution, and could be possible if we made preflights public artifacts that could be fetched without a license, and move preflight checks to the CLI (using Troubleshoot.sh.